Valorization of PES textile waste through glycolysis and aminolysis using bimetallic ZnO and carbon nitride nanocomposites

doi:10.21203/rs.3.rs-3458558/v1

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Research Article

Valorization of PES textile waste through glycolysis and aminolysis using bimetallic ZnO and carbon nitride nanocomposites

https://doi.org/10.21203/rs.3.rs-3458558/v1

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published 28 Jan, 2024

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Polyester (PES) textile fabrics are chemically recycled through aminolysis, and glycolysis catalyzed by nanocomposites composed of Sb (or) In-doped ZnO and g-C₃N₄ nanocomposites prepared by the wet-impregnation method. The nanocomposites were characterized by XRD, UV‒Vis, FT-IR, and SEM-EDS techniques. X-ray diffraction patterns as well as SEM EDS showed the presence of amorphous g-C₃N₄and doped ZnO. The extent of the optical band gaps of ZnO observed in doping with g-C₃N₄. The optical band gap of 3.31 eV of ZnO was reduced to 2.55 to 2.65 eV after doping with g-C₃N₄. SEM morphological analysis showed a sheet-like structure along with ZnO nanoparticles adsorbed on the surface of g-C₃N₄. Glycolysis and aminolysis of colored PES waste produced BHET and BHETA, respectively, as pure monomers in excellent yield (>90%). FT-IR, MS, ¹H, and ¹³C NMR were used to confirm the formation of BHET and BHETA.

Aminolysis

circular economy

chemical recycling

glycolysis

heterogeneous catalyst

PES textile waste

Polyester textile waste was recycled using a green catalyst made from g-C₃N₄ and bimetallic ZnO, achieving a circular economy.
The depolymerization of PES can be achieved through aminolysis and glycolysis methods using ethanolamine and ethylene glycol.
Colored PES textile wastes depolymerized into colorless monomers, BHETA.

Thermoplastic materials, particularly polyethylene terephthalate (PET), provide advantages since they are widely used for various applications, especially in clothing industries. PET demand is rapidly increasing globally due to its low production cost and reproducibility, which benefits the textile industry as well as consumers and is often a better alternative than other materials [1]. Even under challenging circumstances, PET recycling will be successfully adapted by 2020 to provide safe and sustainable solutions to society. The PET polymer plastic production globally increased from 1.5 million tons in 1950 to 367 million tons in 2020. As a result, global plastic production is continually growing and is expected to reach 34 billion metric tons by 2050 [2]. This includes most packaging waste, beverage bottles, polyester textile waste, and various plastic wastes disposed of in nature either by landfilling or incineration. PET is indeed a low-cost commercial polymer that is also one of the most popular semicrystalline thermoplastic types of synthetic polymers among mechanical, electrical, and thermal properties [3].

PET waste plastics have the advantage of being recycled for textile industries and reducing PET waste disposal. PET is recycled in four main categories: 1. Primary (re-extrusion), 2. Secondary (mechanical), 3. Tertiary (chemical), and 4. Quaternary (energy recovery) [4, 5]. PET wastes are depolymerized by alcoholysis, hydrolysis, glycolysis, aminolysis, and ammonolysis. The depolymerized product of glycolysis is bis(2-hydroxyethyl) terephthalate (BHET) [6, 7]. In addition, the use of glycolysis can be done using diethylene glycol, propylene glycol, and dipropylene glycol was also reported [8]. Aminolysis is another method of the PET depolymerization process, which produces primary bis (2-hydroxyethyl) terephthalamide [9]. The chemical recycling process is suitable for the degradation of PET plastic waste for product diversity applications [10]. The perspective of the circular economy as a sustainable approach to management in the textile sector provides a real possibility for recycled and reused PES textile waste to produce fiber for the manufacture of textile products [11–14]. The large amount of PET polymer waste recycled by chemical recycling is an example considered by the circular economy [15, 16].

Zinc oxide is unique and most promising when compared to other oxides because of its semiconducting and photocatalytic activity [17]. Zinc oxide (ZnO) and synthetic polymeric fibers such as PET and nylon showed excellent visible and infrared photocatalyst decomposition efficiency [18–22]. The self-degradable textile-impregnated Ag@ZnO nanocomposite showed good photocatalytic degradation activity under UV‒visible light. Earlier investigations have proven that ZnO exhibits photocatalytic applications under UV light [23, 24]. ZnO is a semiconductor metal oxide with a band gap of 3.37 eV and an excitation binding energy of 60 meV [25]. The band gap tuning of zinc oxide (ZnO) semiconductors is preferred to achieve photocatalytic activity, although it is an efficient material [26–34].

Graphite carbon nitride g-C₃N₄ is a unique sheet-like amorphous semiconductor polymer with a tunable band gap. Because of its unique surface morphology, it has become one of the most widely recognized photocatalysts used for the degradation of hydrocarbons and oxygenation. For instance, g-C₃N₄ doped with metals such as CDs/g-C₃N₄/SnCl₂ and Sb₂WO₆/g-C₃N₄ has a band gap that can absorb visible light for electron-hole stimulation [35, 36]. The nanocomposites of ZnO/g-C₃N₄ resulted in an improved optical gap [37, 38]. g-C₃N₄ has an excellent electrical structure, with a tunable band gap by choosing the synthesis method and g-C₃N₄ [39, 40]. Moreover, the band gap of g-C₃N₄ is useful in the hydrogen evolution reaction under UV‒Visible light [41]. Even though all this photocatalytic activity of pristine g-C₃N₄ is reduced by weak van der Waals interactions among the surrounding g-C₃N₄ layers and the strong generation of photoinduced electron holes, narrow visible light absorption limits its massively successful applicability [42–44]. Visible light photocatalysts of g-C₃N₄ have proceeded with the framework impregnation of metal oxides to nonmetal oxides such as metal oxides, sulfides, oxy sulfides, or oxynitrides. The g-C₃N₄/ZnO nanocomposites promote electron-hole transfer and enhance photocatalytic hydrogen transformation and PET polymer degradation [45]. g-C₃N₄/ZnO can assist in enhancing the absorption, mechanical, and hydrothermal capabilities of ZnO nanoparticles [46]. In addition, g-C₃N₄/ZnO nanomaterials reported excellent dye degradation [47].

In the current investigation, PET wastes are depolymerized using glycolysis and aminolysis reactions. Heterogeneous catalysts such as g-C₃N₄/In-ZnO and g-C₃N₄/Sb-ZnO nanocomposite materials were prepared by the sol-gel method and doped with 2 mol% bimetallic ZnO nanoparticles. These catalysts were characterized by XRD, FT-IR, UV‒Vis, and SEM‒EDS analysis. The PET and depolymerization were optimized concerning parameters such as PET-to-catalyst ratios, MW irradiation, and solvent temperature for aminolysis and glycolysis reactions. The monomers BHETA and BHET were characterized using ¹H, ¹³CNMR, FT-IR, and mass spectral analysis.

2.1 Materials

Zinc nitrate hexahydrate, melamine, indium(III) chloride, antimony trichloride, diethyl amine, ethanol, ethylene glycol, sodium hydroxide, ethanolamine, ethyl acetate, acetone, n-hexane, and other chemicals were purchased from Loba, SRL Pvt., Ltd. (India) and used without further purification. The postconsumer PES textile waste obtained from 100% pure polyester of color threads, red, blue, and green (make: Vardhaman) whose thickness is 100 µm, is cut into coarse threads. All the glassware and quickfits used for experiments were made of corning/borosilicate glass and, before use, washed thoroughly and dried in a hot air oven.

2.2 Synthesis of Catalyst

2.2.1 Pure graphene carbon Nitride (g-C₃N₄) Catalyst

Approximately 10 g of melamine was placed in a silica crucible covered with a lid and used for direct heating at 550°C with a heating ratio of 5°C min^− 1 in a muffle furnace (Linear Enterprises, Chennai). After continued heating for 3 hours, approximately 3 g of pure g-carbon nitride was obtained as a yellowish powder.

2.2.2 Synthesis of In- and Sb-doped ZnO nanoparticles

The indium- and antimony-doped zinc oxides, In-ZnO and Sb-ZnO nanoparticles were synthesized by the sol-gel method. Initially, Zn(NO₃)₂. 6H₂O (0.1 m) starting with 3.0 mol% (3 mmol) In(III) dissolved in 50 mL distilled water and stirred for 15 min at room temperature. Then, 30 ml of diethyl amine and 2 N NaOH were added dropwise using a burette to maintain the base condition of pH at 11. After that, the viscous solution was stirred for 5 hours at 80°C. A milky white precipitate was obtained, filtered, and washed three times (3×100 mL) using deionized (DI) water. The synthesized bimetallic ZnO NPs were kept in an oven to dry at 80°C for 24 h. After drying, the resulting white solid was well-grained into powder form using a mortar and pestle. The crushed powder was calcinated in a static air furnace at 500°C for 1 h. The resulting 2 mol% metal-doped ZnO was stored in an airtight container and kept in a desiccator. Similarly, bimetallic ZnO NPs with 2 mol% antimony were prepared by the same procedure.

2.2.3 Preparation of the g-carbon nitride-doped bimetallic ZnO catalyst

Approximately 2 g of pure g-C₃N₄ catalyst was placed in a 250 ml beaker, and 200 mg (10 wt%) of 3 mol% In/Sb-doped ZnO was added to a beaker containing 50 mL of ethanol. The magnetic solution was stirred well at 60°C for 5 hours. The ethanol was evaporated into a dry state. Finally, 2 mol% IZO (In/ZnO) doped into the g-C₃N₄ catalyst was kept well-grained using a mortar and pestle. A similar procedure was followed for the synthesis of 2 mol% SZO (Sb/ZnO)-doped g-C₃N₄.

2.3 Catalytic activity of g-C₃N₄ doped with indium and antimony-doped ZnO

The catalytic activity of 3 mol% indium/antimony zinc oxide doped with g-carbon nitride IZO, SZO nanocomposites tested for depolymerisation polyester (PES) threads. In this investigation, ethylene glycol is a glycolytic agent, and ethanolamine is aminolyting agent used for depolymerisation under microwave irradiation. The aminolysis and glycolysis reactions of the PES textile afforded the depolymerized final products bis(2-hydroxyethyl) terephthalamide (BHETA) and bis(2-hydroxyethyl) terephthalate (BHET), respectively (Scheme 1).

2.3.1 Aminolysis of PES textile waste under microwave irradiation

The depolymerization of PES textile waste color (red, blue, and green) threads by aminolysis promoted by IZO/g-C₃N₄ and AZO/g-C₃N₄ catalysts under microwave irradiation. One gram of PES threads cut into small pieces was placed in 100 mL Erlenmeyer flasks, and 20 mL of ethanolamine was added. The mixture was irradiated with microwave power set to 180 W at the temperature measured and continued for 2 minutes at 125–150°C. The reaction cycle ran for 2 minutes, PES threads were dissolved in EA, and 50 mg of IZO/g-C₃N₄ or AZO/g-C₃N₄ catalyst was added. In every reaction cycle, the reaction mixture was well shaken and continued for MW irradiation. After a few cycles, 1 mL of the reaction mixture was dissolved in acetone and monitored for reaction progress using precoated TLC plates (20×20 cm, E-Merck, UK, Silica gel G₆₀ F₂₅₄ indicator) and n-hexane – ethyl acetate (70:30) as eluent. Furthermore, BHET and BHETA compounds were confirmed by spectral analysis ¹H, ¹³C NMR, FT-IR, and MS spectroscopy. After the reaction was completed, 50 mL of distilled water under hot conditions was added, followed by filtration to separate the catalyst using Whatman filter paper. The homogeneous reaction mixture was heated at 70°C for 20 min 15–20°C for 12–16 h. Finally, the aminolytic compound of BHETA was obtained, yielding yellowish-white needle-shaped crystals. The yield was dried in a hot air oven at 80°C to calculate the BHETA yield.

2.3.2 Glycolysis of PES textile waste under microwave irradiation

The (red, blue, and green) PES textile threads were depolymerized using ethylene glycol (EG) under microwave irradiation. Approximately 1 g of PES threads was transferred to 100 mL Erlenmeyer flasks containing 20 mL of ethylene glycol (EG). The mixture was shaken well and irradiated at 300 W microwave power for approximately 2 minutes. The temperature of the reaction mixture slowly increased to 180–200°C upon 3 cycles of MW irradiation. After the complete dissolution of PES threads, 50 mg of IZO/g-C₃N₄ or AZO/g-C₃N₄ was added to the reaction mixture. After a few excess cycles, 0.5 mL of the reaction mixture was diluted in acetone, and the progress of the reaction was monitored using aluminum precoated TLC plates (E-Merk, UK, Silica gel G60 F254 indicator) and an n-hexane and ethyl acetate (70:30) solvent mixture. The reaction mixture was diluted with 100 mL of distilled water, and the catalyst was recovered by filtration. Therefore, the final product was a fully water soluble and separated by extraction with chloroform from water solution, and BHET was isolated. All procedures were glycolysis PES waste degradation and depolymerization processes.

The yield of BHETA and BHET and conversion of the PES textile waste degradation percentage determined by the equation

PET degradation (%) = \(\frac{W1-W2}{W2}\times 100\%\) (1)

The yield of aminolysis (BHETA) and glycolysis (BHET) was calculated using

BHETA yield (%) =\(\frac{{W}_{BHETA}}{{W}_{BHETA,0}}\times 100\)

BHET Yield (%)\(=\frac{{W}_{BHET}}{{W}_{BHET T,0}}\times 100\)

W _BHETA/W_BHET and W_BHETA,0/ W_BHET,0 are the experimental weights of BHETA and BHET and the respective theoretical weights. MW_BHETA, MW_BHET, and MWPET are the molecular weights of BHETA (251 g/mol), BHET (254 g/mol), and PET (192 g/mol) repeating units, respectively.

2.4 Characterization of catalyst and depolymerized products

2.4.1 XRD

The crystallite size of pure g-C₃N₄ and g-C₃N₄ doped with 10 wt% indium and antimony with zinc oxide nanoparticles was analyzed by an X-ray diffractometer using a graphite monochromator and Cu K\(\alpha\) as the source operating at 40 kV. XRD analysis was performed using a PAN analytical Empyrean diffractometer (Netherlands) ranging between 2\(\theta\) angles of 20 and 80°.

2.4.2 FT- IR

FT-IR analysis was performed for the identification of functional groups present in pure and doped g-C₃N₄ catalysts and PES textile waste depolymerized products. FT-IR spectra of the catalysts, BHETA and BHET recorded FT-IR (Model: IRTRACER 100, SHIMADZU, Japan) using a solid sample of KBr pellets.

2.4.3 UV‒Vis

By using UV‒Vis spectral analysis, the absorption maxima and optical band gap of pure and doped g-C₃N₄ catalysts were determined. The electronic spectrum recorded using a UV‒Visible spectrometer (Model: UV3600 PLUS, SHIMADZU, Japan) has a UV‒Vis wavelength range of 200–800 nm in the solution state.

2.4.4 SEM Analysis

The SEM studies revealed the morphological and average particle sizes of the pure and In-ZnO/g-C₃N₄ catalysts. Field emission scanning electron microscopy images were recorded (Model: FESEM apreo S, Thermo Fisher Scientific, Netherlands) together with energy dispersive spectroscopy (EDS). Minimum and maximum particle sizes were calculated in pure graphite carbon nitride and silver-doped zinc oxide nanoparticles for the resolved ImageJ software version (version 1.53 K).

3.1 Characterisation of nanocomposites

3.1.1 XRD Analysis

The XRD patterns of pure g-C₃N₄ (VSA01) ZnO, Sb-ZnO/g-C₃N₄ (VSA05), In-ZnO/g-C₃N₄ (VSA06), and the catalyst are shown in Fig. 1. The pristine pure g-C₃N₄ showed a diffraction peak at a 2\(\theta\) angle of 27.37° pertaining a plane of (100) revealed sheet like morphology. The 10 wt% doping In-ZnO/g-CN diffraction intensity peak at 2\(\theta\) angle 27.17˚, is due to the plane (100) of g-C₃N₄. According to the XRD diagram, Sb-ZnO/g-C₃N₄ had well-matched diffraction peaks of [JCPDS NO. 35.0732], indicating that the crystalline structure of the antimony (Sb) nanostructure was identical to that of pristine antimony oxide. It was found that the intensity of the diffraction peak is 28.50°, corresponding to the crystal plane range of (012) [48].

The pure and doped bimetallic (antimony, indium) ZnO nanoparticles observed diffraction peaks at 2\(\theta\)= 27.70˚, 31.40˚ and 34.30˚, with high intensity related the plane (100), (002), (101), and peaks with lower intensity observed at 2\(\theta =\) 36.34˚, 47.50˚, 56.70˚, and 63.35˚ it correspond plane (102), (110), (103) and (112) related to hexagonal wurtzite crystalline pattern of ZnO. The doping of 10 wt% antimony and indium metal oxide nanocomposites did not affect the pure g-C₃N₄ and zinc oxide wurtzite hexagonal structure, and the incorporation of doped metal oxides is clearly shown. Lattice parameters, cell volume and crystallize size of the nanocomposites calculated using Debye-Scherrer and Williamson-Hall method summarised in Table 1.

Table 1

Lattice parameters, crystalline size, and lattice parameter strains using the Scherrer and Williamson Hall equation for g-C₃N₄, Sb-ZnO, and In-ZnO-doped g-C₃N₄.
Material	Lattice parameters			Volume (nm³)	Crystalline size (nm) (Scherrer equation)	Crystalline size (nm) (W-H equation)
Material	a (A°)	c (A°)	c/a	Volume (nm³)	Crystalline size (nm) (Scherrer equation)	Crystalline size (nm) (W-H equation)
g-C₃N₄ (VSA01)	1.54	6.47	4.18	13.79	87.17	159.13
10wt% of Sb-ZnO/g-C₃N₄ (VSA05)	1.60	6.45	3.24	12.47	90.89	42.71
10wt% of In-ZnO/g-C₃N₄ (VSA06)	1.54	6.47	3.64	11.65	90.88	96.54

The average crystalline size of a pure g-C₃N₄ and indium- and antimony-doped ZnO sample is calculated using Debye-Scherrer's formula, which seems given by

n\(\lambda =2d Sin\theta\) ……… (1)

D = K\(\lambda /\beta Cos\theta\) ……… (2)

where K is the shape factor, \(\lambda\) is the wavelength of the X-rays, \(\beta\) is the FWHM of the prominent Bragg peak in radians, and \(\theta\) is the Bragg angle in degrees [49].

Williamson-Hall (W-H) plotting is among the most effective and simple methods for calculating alteration in particle size and micro strain due to doping. A diagram is drawn between \(\beta\)cos\(\theta\) in y-axis and 4\(\epsilon\)sin\(\theta\) in x-axis to determine the crystallite size of pure and doped metal oxides. In and Sb containing ZnO nanoparticles using the W-H plotting. The W-H plot method is used to determine the average particle size and lattice strain by applying the formula,

βcos\(\theta\) = 4\(\epsilon\)sin\(\theta\) + (K\(\lambda\)/ D)……. (3)

\(\beta\) is FWHM of diffraction peaks, K − 0.9 (shape factor), \(\lambda\) 1.5406 (wavelength of the X-ray source), D is crystallite size, and \(\theta\) is Bragg peak position. Formula (3) can be signified as a straight line with the gradient slope "\(\epsilon\)' calculated from the straight line's slope and from the intercept, K\(\lambda\)/D can provide average particle size. The W-H equation is utilized to calculate lattice parameters, strain, and average crystallite size [50].

3.1.2 Absorption maxima and optical bandgap

UV‒Vis light absorption analysis of g-C₃N₄ and 3 mol % indium-doped zinc oxide and antimony zinc oxide prepared by the sol-gel method. Pure g-C₃N₄ (VSA01), g-C₃N₄/Sb-ZnO (VSA05) and g-C₃N₄/In-ZnO (VSA06) of lamellar nanosheets in 10 wt% doped ZnO. UV‒vis light analysis was performed on the samples, and the UV-Vis absorption spectra and Tauc’s plot are shown in Fig. 2(a) and (b), respectively. In Table 2, absorption maxima and calculated optical bandgap summarised. The pristine g-C₃N₄ light absorption extends from the ultraviolet region to the visible light region, and the light absorption edge is approximately 200–500 nm. This corresponds to an energy band gap of approximately 2.7 eV [51].

Indium zinc oxide graphene carbon nitride (In-ZnO/g-C₃N₄) and another g-C₃N₄-doped metal oxide, antimony zinc oxide, have absorption ranges of 295–333 and 350–450 nm, and their corresponding energy band gap ranges of pure zinc oxide calculated to be 3.18 eV, g-C₃N₄ (VSA01) to be 2.79 eV, antimony-doped zinc oxide (VSA05) to be 2.82 eV, and indium-doped zinc oxide with g-C₃N₄ (VSA06) to be 2.81 eV. These, 10 wt% metal oxide doped with graphitic carbon nitride samples have well-defined broad absorption peaks that correspond to the both g-C₃N₄ as well as doped ZnO. The UV‒Vis spectral analysis of of 10 wt% Sb and In with ZnO nanocomposites, and these materials had a high impact on the photocatalytic properties of the materials in the visible region while comparing with pristine ZnO.

Table 2

UV‒Vis absorption maxima values, optical band gap, FT-IR regions, and SEM‒EDS metal doping atomic & weight percentages Fi
Material	Absorption maxima (λ, nm)	Optical band gap (eV)	Wavenumber (cm^− 1)	FT-IR assignments	Weight (%)	Atomic (%)
g-C₃N₄ (VSA01)	385	2.7	700–810	C-N	C-31.67 N-68.33	C-35.09 N-64.91
g-C₃N₄/Sb-ZnO (VSA05)	375	2.82	700–810 1120–1245	C-N Sb-ZnO	C-33.01 N-48.12 O-13.21 Zn-5.45 Sb-0.21	C-38.74 N-48.42 O-11.64 Zn-1.18 Sb-0.02
g-C₃N₄/In-ZnO (VSA06)	370	2.81	700–810 1295–1345	C-N In-ZnO	C-28.51 N-59.43 O-8.61 Zn-3.18 In-0.21	C-32.99 N-58.85 O-7.47 Zn-0.67 In-0.03

3.1.3 FT-IR spectroscopy

The molecular structure information of the g-C₃N₄/In-ZnO and g-C₃N₄/Sb-ZnO samples analysed by FT-IR characterization is shown in Fig. 3 and values are given in Table 2. The FT-IR spectrum recorded in the transmittance mode in the wavenumber range of 400–4000 cm^− 1. The spectra showed bands at 800, 1120–1245, 1390, 3000 and 3200 cm^− 1.

The peaks of pristine g-C₃N₄ showed prominently in nanocomposites, VSA05 (g-C₃N₄/AZO) and VSA06 (g-C₃N₄/IZO) with characteristic peak bands at 1130–1740 cm^− 1. These regions are related to the typical C-N stretching mode of the g-C₃N₄ heterocyclic, and the peaks at 1120–1245 cm^− 1 and 1290–1345 cm^− 1 are attributed to C-N stretching vibrations. The characteristic sharp peak at 800–810 cm^− 1 is attributed to the out-of-plane bending vibration of the triazine ring. The broad peaks between approximately 2790–3500 cm^− 1 originated from the tensile vibrational modes of -NH and -OH groups observed in H₂O [52, 53]. The pristine characteristic peak in the FT-IR spectra of the prepared g-C₃N₄/In-ZnO and g-C₃N₄/Sb-ZnO samples showed the structure of g-C₃N₄ maintained well after doping. These results indicate that the doped ZnOs are successfully supported on the g-C₃N₄ nanosheets.

3.1.4 SEM with EDS analysis

SEM-EDS analysis was used to investigate the surface morphology and chemical composition of pure g-C₃N₄, g-C₃N₄/Sb -ZnO, and g-C₃N₄/In-ZnO. Figures 4 and 5 show the SEM images and EDS analysis of In and Sb doped ZnOs and surface composition detected by EDS analysis of composite materials, respectively. The atomic and weight percentage of elements present in the nanocomposites summarised in Table 2. The nanocomposite surface contains small fractures and holes due to the integration of ZnO nanoparticles into the polymer matrices of transition metals. The main components identified by EDS analysis are Sb, In and C, N, O. The existence of a peak in the EDS spectrum for Zn confirms that the nanomaterials have been effectively loaded into the structural system after the nanocomposite surface has been transformed together into smooth, compact, and heterogeneous surfaces by the molecular protective layer. Sb and In doped ZnO showed the presence of 3.85 wt% of Sb and In in ZnO with respect to Zn(II). In addition, when comparing with Zn(II), the dopants Sb and In present in 1.69 and 4.47 at% respectively.

3.2 Optimization of aminolysis and glycolysis of PES textile wastes

Depolymerization of red, blue, and green polyester (PES) textiles was studied by aminolysis and glycolysis under microwave irradiation. The catalytic activity of heterogeneous catalysts, g-C₃N₄/IZO and g-C₃N₄/AZO compared to pure g-C₃N₄ catalyst. The structure of g-C₃N₄ is a carbon and nitrogen-conjugated sheet-like system. It is capable of absorbing light in the visible range at 400–425 nm. The occurrence of a nitrogen lone pair, in addition to a cavity developed throughout the melamine source polycondensation reaction, serves as a carrier site for Lewis acidic doped ZnO nanoparticles. The objective of producing a doped nanocomposite with g-C₃N₄ is to depolymerize PES-colored threads as degraded dyes in a one-pot reaction to obtain aminolysis and glycolysis chemolysis depolymerized products BHETA and BHET, respectively. Depolymerization reaction parameters such as microwave irradiation power, time, and catalyst recycling studies.

3.2.1 Effect of Catalyst Activity

Figure 5a showed investigations of the pure sample g-C₃N₄ and 10 wt % doped antimony and indium with ZnO. One gram of red, blue, and green PET color threads was treated with 100 mg of the nanocomposite catalyst (10:1 PET:catalyst ratio). Degradation and depolymerization studied by aminolysis and glycolysis chemical recycling methods under microwave irradiation conditions with different parameters. In our investigation, PET and catalyst ratio, PET to solvent ratio, microwave input, irradiation time as well as reaction cycle were optimized to achieve the maximum yield of BHETA from aminolysis and BHET from glycolysis. While comparing with pure g-CN, ZnO doped g-CN showed better catalytic activity due to Lewis acidic sites created by bimetallic ZnO nanoparticles.

3.2.2 Effect of Microwave power

PES textile waste threads degradation and depolymerization using different MW power for aminolysis and glycolysis was studied (Fig. 5b). For glycolysis PES textile waste decomposition process evaluated at 8 different MW power and yield of BHETA was noted. The MW irradiated at 100, 200, 250, 300, 350, 400, and 500 W power. Starting MW power 100 gave the lowest yields (45%). At a MW power of 300 W, temperature reaches up to 180°C, the PES textile was completely dissolved within 5–7 min, and a high yield (94%) of BHET was obtained. We identified glycolysis PES textile decomposition parameters to 300 W (180°C) and set all glycolysis further reactions. The aminolysis MW 8 different powers were 25, 50, 100, 150, 180, 200, 220, and 250 W. When 180 W was reached, the PES textile was fully dissolved at 140°C, and the maximum yield (95%) was obtained for BHETA, which was set as the aminolysis reaction parameters.

3.2.3 MW irradiation time

Figure 5c is depicted the effect of microwave irradiation for aminolytic (EA) and glycolytic (EG) solvents uses the PES textile waste degradation process. A total of 500 mg of PET threads (red, blue, and green) and 20 ml of aminolysis/glycolytic (EA/EG) solvent were set to the MW power, and the chemical treatment time of the PET waste threads was monitoredand decreased with increasing starting time. The aminolysis irradiation process parameter time range was 1, 2, 5, 8, 10, 15, 20, and 25 min to run the degradation process. When 5 min, the reaction should be completely dissolved in PES textile degradation, 50 mg of Sb & In/ZnO-g-C₃N₄ catalyst should be added, and the reaction should be run for 15 min to complete; the highest BHETA yield (95%) is present compared to the other time parameter ranges. The glycolysis PES textile waste decomposition time rangewas (5, 15, 30 mins, 1, 2, and 3 hrs). When 1 h of reaction was completed, the maximum yield (94%) of BHET was obtained. All the above procedures for glycolysis and aminolysis PES textile degradation MW irradiation time range is determined for enormous factor.

3.2.4 Effect of PET to Solvent ratio

The effect of PET to catalyst ratio of 1 g of PET and 100 mg of nanocomposite catalyst with various amounts of solvent to proceed with chemical recycling aminolysis ethanolamine (EA) and glycolysis ethylene glycol EG depolymerization methods (Fig. 5d). One gram of PET and glycolytic and aminolysis solvents was increased from 5, 10, 15, 20, to 25 ml to optimize the MW in aminolysis at 180 W and glycolysis at 300 W, respectively. The yield of the aminolysis product (BHETA) obtained was 49, 62, 73, 86, and 95%, and the glycolysis product was obtained at approximately 46, 54, 66, 84, and 92%, respectively, for 5, 10, 15, 20, and 25 ml of EA and EG solvents in both the aminolysis and glycolysis reactions.

3.2.5 Catalyst Recycling Studies

Study of catalyst recycling and reuse for aminolysis and glycolysis under microwave power using Sb-ZnO/g-C₃N₄ as a heterogeneous catalyst (Fig. 5e). After completing the aminolytic and glycolytic reaction, 100 mL of distilled water was added to the hot condition for the filtration step using Whatman filter paper filtration. The catalyst was washed with deionized water dry in a hot air oven at 80°C. These catalysts are ready for further depolymerization reactions for 5 to 9 cycles and are reused because the catalyst yield is more than 90%. The In-ZnO/g-C₃N₄ catalyst was characterized by SEM.

3.3 Decolorization of pure polyester (PES) color threads

The PES (red, blue, and green) color threads were cut into small pieces, and approximately 1 g of PES threads was placed in a 100 mL Erlenmeyer flask. 20 mL of ethanolamine or ethylene glycol was added. The aminolysis chemical recycling MW irradiation power was 180 W or 80–100°C, and the glycolysis MW power was 300 W or 180–200°C for PES degradation. Each cycle was run for 2 min after that time interval, and the solution was well shaken for hot conditions. After a few cycles of running, the PES starts to degrade slightly separately from the PES threads. The aminolysis reaction was performed for 30 mins, and glycolysis was performed for 1 hr for complete dye decolonization and depolymerization. Red thread is a very strong dye that does not change dye degradation. Blue thread is dye changed to a deep reddish pink color, and green thread dye is converted to a deep yellow color after dye degradation with every step for picture proof. Since deionized hot water (50 mL) was added to the solution, it was filtered and separated for the catalyst. A few hours later, needle-shaped crystals (red‒reddish, blue and green‒white crystals) formed and were converted into monomer BHETA, and BHET was confirmed by further spectral analysis by FT-IR, ¹H, ¹³C-NMR, and MS analysis (Fig. 6).

3.4 Spectral characterization of BHETA and BHET

The complete depolymerization of PES waste color (red, blue, green) threads treated with chemical recycling methods aminolysis (EA) and glycolysis (EG) solvents degradation and depolymerized MW irradiation to produce single monomer compounds of aminolysis compound is bis (2-hydroxyethyl) terephthalamide (BHETA) and glycolysis depolymerized product is bis (2-hydroxyethyl) terephthalate (BHET). These monomer compounds were confirmed with the chemical structure used for spectral characterization, such as Fourier transform (FT-IR) spectroscopy (Fig. 7(a) & (b)), nuclear magnetic resonance (¹H, and ¹³C- NMR) spectroscopy of BHETA and BHET given in Figs. 8(a) & (b) and 9(a) & (b)), and ESI-mass spectrometry of BHETA and BHET (Fig. 10(a) and (b)).

3.4.1 FT-IR spectrum analysis BHETA and BHET

The distinctive feature chemical bond in PES along with the purified monomer was determined using FT-IR spectroscopy (Table 3). The IR spectra of PES before and after decomposition were compared with the standard's IR spectra and compared with the IR spectra of the requirement to investigate the nature of chemical bonds introduced in the isolated compound. Figure 7 (a) represents the FTIR spectrum of isolated BHETA and the starting material (PES) before degradation. The revealed IR values are fairly consistent with the results obtained.

Table 3

FT-IR band stretching and vibrations of the BHETA and BHET
S.no	Band name	BHETA (cm^− 1)	BHET (cm^− 1)
1	OH Stretching	3364, 3291	3447
2	-CH Aromatic	2852	2880
3	-CH₂- Aliphatic	2967	2963
4	-C = C-	1501	1456
5	carbonyl	1630 (amide carbonyl)	1717 (ester carbonyl)
6	-CH Aliphatic	1053

The infrared spectrum details of bis(2-hydroxyethyl) terephthalamide modes of aliphatic and aromatic stretching and vibration regions (cm^− 1) are shown in Table 3. The FT-IR spectrum showed a 400–4000 cm^− 1 alcohol or hydroxide water molecule peak at 3291–3364 cm^− 1, and other regions presented aliphatic –CH₂- and aromatic –CH at 2967 cm^− 1 and 2852 cm^− 1. The aromatic –C = C- peak at 1501 cm^− 1, functional group amide carbonyl group present at 1630 cm^− 1, and aliphatic –CH at 1053 cm^− 1 peaks confirmed the BHETA compound in the FT-IR spectrum.

As opposed to Fig. 7(b), the PES infrared spectra are shown after thermal decomposition. The lengths of the PES chains are degraded and converted to monomer BHET. That kind of will produce a variable number of modified (-CH) groups to significant changes in band intensity Moreover, in the figures to infrared spectrum indicating the presence of -OH groups associated with oligomer establishment in the 3447 cm^− 1 bands (hydroxyl and alcohol end of the chain) Chemical bonds were attempting to break between groups) and the monomer BHET. PET glycolysis with ethylene glycol produces mostly monomer BHET [53]. The PES textile waste after degradation and depolymerization of the final product was isolated (BHET), with an OH stretching appearance at 3447 cm^− 1 and asymmetric stretching at 2880–2963 cm^− 1. Ester carbonyl presence at 1717 cm^− 1 and aromatic -C = C- stretching at 1456 cm^− 1. These regions were confirmed with monomer bis (2-hydroxyethyl) terephthalate (BHET).

3.4.2 ¹H and ¹³C NMR Spectrum of BHETA

The ¹H-NMR spectrum of the PES waste color (red, blue, and green) threads treated with aminolysis using ethanolamine depolymerization of the final product BHETA is given in the supplementary information in Fig. 8(a). The main product N¹, N⁴- bis (2-hydroxyethyl) terephthalamide (BHETA) symmetrical molecule (-NH-CO-) proton presents a triplet peak at 8.57 ppm. Since four aromatic protons appeared, a sharp singlet peak at 7.93 ppm (C1, C2, C4, and C5) in the central aromatic phenyl ring of BHETA was confirmed. Aliphatic –CH₂-CH₂- protons are present between 3.32 and 3.56 ppm. The hydroxyl (-OH) group protons (C11 and C12) are observed at 2.46 to 2.57 ppm in a triplet. Therefore, the indication of amide (-NH) and hydroxyl alcoholic group (-OH) protons confirms PES waste using ethanolamine to completely depolymerize and convert to form BHETA.

The ¹³C NMR spectrum in the supplementary information of the analyzed product, BHETA, is shown in Fig. 8(b). At 166.21 ppm, the amide carbonyl carbon of BHETA appeared, indicating that the amide carbonyl has a structure that confirms the symmetrical nature of the BHETA single product. Even though BHETA is a symmetrical molecule, two aromatic carbons were detected at 137.14 and 127.61 ppm. The peak at 137.14 ppm corresponds to C-1 and C-4 attached to amide carbonyl, and the peak at 127.61 ppm corresponds to C-2, C-3, C-5, and C-6 attached to hydrogen, both of which appeared as singlets with high intensity. At 42.73 ppm, BHETA showed two -CH₂- carbons of the aliphatic chain attached to amide -NH-. At, the second hydroxyl group linked to carbon -CH₂ appeared at 60.16 ppm of BHETA.

3.4.3 ¹H and ¹³C NMR Spectrum of BHET

The glycolysis depolymerized product BHET was confirmed by ¹H NMR spectrum analysis, as shown in Fig. 9(a). The singlet sharp peak appearance of four aromatic protons attached to C1, C2, C3, and C4 at 8.14 ppm confirmed that glycolysis completely depolymerized PES waste to the BHET monomer single compound. BHET investigated two hydrogens attached to carbons C9 and C10. In addition, ester carbonyl (-CH₂-OC = O) C7 and C8 oxygens are present at 4.98–5.01 ppm. The other four hydrogens connected to (C11 and C12) CH₂ and OH appeared at 4.23–4.48 ppm. Moreover, the hydroxyl group attached to -CH₂- appeared as a broad peak at 3.30–3.74 ppm. At 2.51 ppm, deuterated DMSO solvent appeared as a singlet [54].

The ¹³C NMR spectrum of bis(2-hydroxyethyl) terephthalate (BHET) is shown in supplementary material Fig. 9(b). The ester carbonyl carbon of BHET appeared at 165.66 ppm, revealing a single ester carbonyl present in the structure and no additional carbonyl carbons, which confirmed the presence of BHET as a single product. Because BHET is a symmetrical molecule, two aromatic carbons were detected at 134.22 and 129.99 ppm. The peak at 134.22 ppm corresponds to C-1 and C-4 connected to ester carbonyl, and the peak at 129.99 corresponds to C-2, C-3, C-5, and C-6 attached to hydrogen, each of which appeared as singlets with high intensity. The -CH2 - carbons of the aliphatic chain attached to the ester carbonyl oxygen were detected in BHET at 67.50 ppm. The shift in -CH₂ is due to the two -CH₂- groups attached to the chain. Hydroxyl group-connected -CH₂- carbons were detected at BHET at 59.45 ppm [55, 56], but we were unable to account for the peak at 63.26 ppm.

3.4.3 Mass spectrum of BHETA and BHET

Mass spectra of aminolysis- and glycolysis-depolymerized final products obtained from single monomer components from PET chemical recycling methods. Figure 10 (a) shows that the mass spectrum of the aminolysis-depolymerized monomer product is bis(2-hydroxyethyl) terephthalamide (BHETA). The chemical formula of BHETA is C₆H₁₅N₂O_4, with a molecular weight of 251.01 g/mol (M + H). Another peak indicates the formation of Na + from BHETA. The bis(2-hydroxyethyl) terephthalate BHET glycolysis monomer compound molecular formula is C₁₂H₁₄O₆ with a molecular weight of 254.24 g/mol. This aminolysis monomer compound is recorded due to the electron spray ionization (ESI) method.

The mass analysis of the chemically recycled PES (red, blue, and green) waste thread glycolysis depolymerization final product bis(2-hydroxyethyl) terephthalate (BHET) mass spectrum is shown in Fig. 10(b). The molecular formula of the BHET extract is C₁₂H₁₄O_6, and its molecular weight is 254.24 g/mol. The BHET confirmation molecular ion peak is 255.20 g/mol (M + H) protonated form, and the nearest peak is 185.20, indicating the formation of the Na⁺ form of BHET. This spectrum was obtained by the electron spray ionization (ESI) method.

In summary, we synthesized g-C₃N₄ by a direct heating method, and 10 wt% In- and Sb-doped ZnO/g-C₃N₄ nanocomposites were prepared by ultrasonication. The nanocomposites were characterized by XRD, FT-IR, UV‒Vis, and SEM-EDX analysis. The sheet-like structure of pure g-C₃N₄ and the hexagonal wurtzite structure of bimetallic ZnO were observed from the XRD patterns. The electronic spectrum of the nanocomposites revealed that the absorption maxima of ZnO shifted to the visible light region with evidence from the reduction of the optical band gap. The FT-IR spectra show pure g-C₃N₄ and 2 mol% doped metal oxides, with no significant changes in catalysts compared to pure g-C₃N₄. SEM coupled with EDX analysis showed the surface morphology, elemental mapping, and composition of the nanocomposites. Zinc oxide doped with indium and antimony nanocomposites has a Lewis acidic nature that enables them to effectively degrade and depolymerize 100% pure polyester color threads (red, blue, and green) from PET (polyethylene terephthalate) waste. This is achieved through chemical recycling methods such as aminolysis and glycolysis using ethanolamine and ethylene glycol, respectively, at 150–210°C under microwave irradiation. The pure g-C₃N₄, In-ZnO/g-C₃N₄, and Sb-ZnO/g-C₃N₄ heterogeneous nanocomposite catalysts have proven to be potential catalysts owing to their reusability and good conversion of PET polymers and afforded more than 90% yields of BHETA and BHET in 30–90 mins. Furthermore, the final product of BHETA and BHET chemical structure is confirmed with FT-IR, ¹H, and ¹³C NMR and mass spectrometry analysis. Furthermore, the investigation of degradation and depolymerization under UV‒visible conditions using g-C₃N₄-doped cobalt and manganese metal oxide nanocomposites is in progress in our laboratory.

Acknowledgment: Dr. V. Sivamurugan thanks the University Grants Commission (UGC) for providing financial support in the form of a minor research project [File No. F: MRP-6393/16 (SERO/UGC)]. Mr. M Anbarasu is grateful to the Directorate of Collegiate Education in Chennai for the Research Scholarship. Characterizing catalysts and depolymerized products was made possible by the Centralized Sophisticated Instrument Facilities (CSIF), Interdisciplinary Institute of Indian System of Medicine (IIISM), SRM Institute of Science and Technology, Katankulathur - 603 203, and SCIF:SRM Central Instrumentation Facility, NANOTECHNOLOGY RESEARCH CENTRE.

Authors’ Contributions: Investigation and manuscript writing: MA. Resources and methodology: MP. Formal analysis: VV. Supervision: BN. Conceptualization, formal analysis, manuscript writing, and supervision: VS. All authors have read and agreed to the published version of the manuscript.

Conflict of Interest

The authors have declared that they have no conflict of interest.

Ethical Approval

Not applicable

Samples availability

The sample of catalysts and all the depolymerized samples available from the corresponding author.

Funding

Agency: University Grants Commission (UGC), File No. F: MRP-6393/16 (SERO/UGC).

Samak NA, Jia Y, Sharshar MM, Mu T, Yang M, Peh S, Xing J. (2020) Recent advances in biocatalysts engineering for polyethylene terephthalate plastic waste green recycling. Environment International 145:106144. https://doi.org/10.1016/j.envint.2020.106144
Geyer R, Jambeck JR, Law KL (2017) Production, use, and fate of all plastics ever made. Science Advances 3:25–29. https://doi.org/10.1126/sciadv.1700782
Mandal, S., Dey, A., 2019. 1 - PET Chemistry, in: Thomas, S., Rane, A., Kanny, K., V.k., A., Thomas, M.G. (Eds.), Recycling of Polyethylene Terephthalate Bottles, Plastics Design Library. William Andrew Publishing, pp. 1–22. https://doi.org/10.1016/B978-0-12-811361-5.00001-8.
Helmer Pedersen T, Conti F (2017) Improving the circular economy via hydrothermal processing of high-density waste plastics. Waste Management 68:24–31. https://doi.org/10.1016/j.wasman.2017.06.002
Sheel A, Pant D. (2019). 4 - Chemical Depolymerization of PET Bottles via Glycolysis, in: Thomas, S., Rane, A., Kanny, K., V.k., A., Thomas, M.G. (Eds.), Recycling of Polyethylene Terephthalate Bottles, Plastics Design Library. William Andrew Publishing, pp. 61–84. https://doi.org/10.1016/B978-0-12- 811361-5.00004-3.
Guo F, Wang L, Sun H, Li M, Shi W. (2020) High-efficiency photocatalytic water splitting by a N-doped porous g-C₃N₄ nanosheet polymer photocatalyst derived from urea and: N, N -dimethylformamide. Inorganic Chemistry Frontiers 7:1770–1779. https://doi.org/10.1039/d0qi00117a
Payne J, Jones MD. (2021) The Chemical Recycling of Polyesters for a Circular Plastics Economy: Challenges and Emerging Opportunities. ChemSusChem 14:4041–4070. https://doi.org/10.1002/cssc.202100400
Palhano Zanela TM, Curti Muniz E, Policiano Almeida CA. (2018) Chemical recycling of poly (ethylene terephthalate) (PET) by alkaline hydrolysis and catalyzed glycolysis. Electron J Chem. http://dx.doi.org/10.17807/orbital.v10i3.1104.
Leng Z, Padhan RK, Sreeram A. (2018) Production of a sustainable paving material through chemical recycling of waste PET into crumb rubber modified asphalt. Journal of Cleaner Production 180:682–688. https://doi.org/10.1016/j.jclepro.2018.01.171
Pandi N, Sonawane SH, Kola AK, Zore UK, Borse PH, Ambade SB, Ashokkumar M. (2021) Halloysite nanotubes-based supercapacitor: preparation using sonochemical approach and its electrochemical performance. Energy, Ecology and Environment 6:13–25. https://doi.org/10.1007/s40974-020-00174-2
Provin AP, Dutra AR de A, de Sousa e Silva Gouveia ICA, Cubas e. ALV (2021) Circular economy for fashion industry: Use of waste from the food industry for the production of biotextiles. Technological Forecasting and Social Change 169:120858. https://doi.org/10.1016/j.techfore.2021.120858
Wei DW, Wei H, Gauthier AC, Song J, Jin Y, Xiao H. (2020) Superhydrophobic modification of cellulose and cotton textiles: Methodologies and applications. Journal of Bioresources and Bioproducts 5:1–15. https://doi.org/10.1016/j.jobab.2020.03.001
Miao X, Lin J, Bian F. (2020) Utilization of discarded crop straw to produce cellulose nanofibrils and their assemblies. Journal of Bioresources and Bioproducts 5:26–36. https://doi.org/10.1016/j.jobab.2020.03.003
Tayel AA, Ghanem RA, Moussa SH, Fahmi M, Tarjam HM, Ismail N. (2018) Skin protectant textiles loaded with fish collagen, chitosan and oak galls extract composite. International Journal of Biological Macromolecules 117:25–29. https://doi.org/10.1016/j.ijbiomac.2018.05.150
Editorial. Closing the plastics loop. (2018) Nature Sustainability 1:205. https://doi.org/10.1038/s41893-018-0075-3
Rahimi AR, Garciá JM (2017) Chemical recycling of waste plastics for new materials production. Nature Reviews Chemistry 1:1–11. https://doi.org/10.1038/s41570-017-0046
Shaba EY, Jacob JO, Tijani JO, Suleiman MAT (2021) A critical review of synthesis parameters affecting the properties of zinc oxide nanoparticle and its application in wastewater treatment. Applied Water Science. https://doi.org/10.1007/s13201-021-01370-z
Shirgholami MA, Nazari A, Mirjalili M (2015) Statistical optimization of self-cleaning technology and color reduction in wool fabric by nano zinc oxide and eco-friendly cross-linker. Clean Technologies and Environmental Policy 17:905–919. https://doi.org/10.1007/s10098-014-0842-4
Tran Thi VH, Lee BK (2017) Development of multifunctional self-cleaning and UV blocking cotton fabric with modification of photoactive ZnO coating via microwave method. Journal of Photochemistry and Photobiology A: Chemistry, 338:13–22. https://doi.org/10.1016/j.jphotochem.2017.01.020
Upasani PS, Sreekumar T V., Jain AK (2016) Polyester fabric with inherent antibacterial, hydrophilic and UV protection properties. Journal of the Textile Institute 107:1135–1143. https://doi.org/10.1080/00405000.2015.1097082
Monsef R, Ghiyasiyan-Arani M, Salavati-Niasari M (2018) Application of ultrasound-aided method for the synthesis of NdVO₄ nano-photocatalyst and investigation of eliminate dye in contaminant water. Ultrasonics Sonochemistry 42:201–211. https://doi.org/10.1016/j.ultsonch.2017.11.025
Mazloom F, Masjedi-Arani M, Ghiyasiyan-Arani M, Salavati-Niasari M (2016) Novel sodium dodecyl sulfate-assisted synthesis of Zn₃V₂O₈ nanostructures via a simple route. Journal of Molecular Liquids 214:46–53. https://doi.org/10.1016/j.molliq.2015.11.033
Aguirre M, Barrado M, Iturrondobeitia M, Okariz A, Guraya T, Paulis M, Leiza JR. (2015) Film forming hybrid acrylic/ZnO latexes with excellent UV absorption capacity. Chemical Engineering Journal 270:300–308. https://doi.org/10.1016/j.cej.2015.02.025
Mukhopadhyay S, Das PP, Maity S, Ghosh P, Sujatha Devi P. (2015) Solution grown ZnO rods: Synthesis, characterization and defect mediated photocatalytic activity. Applied Catalysis B: Environmental 165:128–138. https://doi.org/10.1016/j.apcatb.2014.09.045
Singh P, Kumar R, Singh RK. (2019) Progress on Transition Metal-Doped ZnO Nanoparticles and Its Application. Industrial and Engineering Chemistry Research 58:17130–17163. https://doi.org/10.1021/acs.iecr.9b01561
Liao Y, Xie C, Liu Y, Huang Q. (2013) Enhancement of photocatalytic property of ZnO for gaseous formaldehyde degradation by modifying morphology and crystal defect. Journal of Alloys and Compounds 550:190–197. https://doi.org/10.1016/j.jallcom.2012.09.109
Wang H, Li J, Ding N, Zeng X, Tang X, Sun Y, Lei T, Lin L. (2020) Eco-friendly polymer nanocomposite hydrogel enhanced by cellulose nanocrystal and graphitic-like carbon nitride nanosheet. Chemical Engineering Journal 386:124021. https://doi.org/10.1016/j.cej.2020.124021
Beura R, Pachaiappan R, Paramasivam T (2021) Photocatalytic degradation studies of organic dyes over novel Ag-loaded ZnO-graphene hybrid nanocomposites. Journal of Physics and Chemistry of Solids 148:109689. https://doi.org/10.1016/j.jpcs.2020.109689
Heidari Z, Alizadeh R, Ebadi A, Pelalak R, Oturan N, Oturan M.A. (2020) Degradation of furosemide using photocatalytic ozonation in the presence of ZnO/ICLT nanocomposite particles: Experimental, modeling, optimization and mechanism evaluation. Journal of Molecular Liquids 319:114193. https://doi.org/10.1016/j.molliq.2020.114193
Zhang C, Fei W, Wang H, Li N, Chen D, Xu Q, Li H, He J, Lu J. (2020). p-n Heterojunction of BiOI/ZnO nanorod arrays for piezo-photocatalytic degradation of bisphenol A in water. Journal of Hazardous Materials, 399:123109. https://doi.org/10.1016/j.jhazmat.2020.123109
Chaudhary K, Shaheen N, Zulfiqar S, (2020) Binary WO₃-ZnO nanostructures supported rGO ternary nanocomposite for visible light driven photocatalytic degradation of methylene blue. Synthetic Metals 269:. https://doi.org/10.1016/j.synthmet.2020.116526
Rosman N, Salleh WNW, Mohamed MA, Harun Z, Ismail AF, Aziz F. (2020) Constructing a compact heterojunction structure of Ag₂CO₃/Ag₂O in-situ intermediate phase transformation decorated on ZnO with superior photocatalytic degradation of ibuprofen. Separation and Purification Technology 251: https://doi.org/10.1016/j.seppur.2020.117391
Yulizar Y, Apriandanu DOB, Ashna RI. (2020). La₂CuO₄-decorated ZnO nanoparticles with improved photocatalytic activity for malachite green degradation. Chemical Physics Letters 755:. https://doi.org/10.1016/j.cplett.2020.137749
Kumari V, Yadav S, Jindal J, Sharma S, Kumari K, Kmar N. (2020) Synthesis and characterization of heterogeneous ZnO/CuO hierarchical nanostructures for photocatalytic degradation of organic pollutant. Advanced Powder Technology 31:2658–2668. https://doi.org/10.1016/j.apt.2020.04.033
Li D, Huang J, Li R, Chen P, Chen D, Cai M, Liu H, Feng Y, Lv W, Liu G. (2021) Synthesis of a carbon dots modified g-C₃N₄/SnO₂ Z-scheme photocatalyst with superior photocatalytic activity for PPCPs degradation under visible light irradiation. Journal of Hazardous Materials 401:123257. https://doi.org/10.1016/j.jhazmat.2020.123257
Ren Y, Li Y, Wu X, Wang J, Zhang G. (2020) S-scheme Sb₂WO₆/g-C₃N₄ photocatalysts with enhanced visible-light-induced photocatalytic NO oxidation performance. Chinese Journal of Catalysis 42:69–77. https://doi.org/10.1016/S1872-2067(20)63631-2
Le S, Jiang T, Li Y, Zhao Q, Li Y, Fang W, Gong M. (2017) Highly efficient visible-light-driven mesoporous graphitic carbon nitride/ZnO nanocomposite photocatalysts. Applied Catalysis B: Environmental 200:601–610. https://doi.org/10.1016/j.apcatb.2016.07.027
Wen P, Sun Y, Li H, et al (2020) A highly active three-dimensional Z-scheme ZnO/Au/g-C₃N₄ photocathode for efficient photoelectrochemical water splitting. Applied Catalysis B: Environmental 263:118180. https://doi.org/10.1016/j.apcatb.2019.118180
Lin L, Yu Z, Wang X (2019) Crystalline Carbon Nitride Semiconductors for Photocatalytic Water Splitting. Angewandte Chemie - International Edition 58:6164–6175. https://doi.org/10.1002/anie.201809897
Zhang L, Long R, Zhang Y, Duan D, Xiong Y, Zhang Y, Bi Y. (2020). Direct Observation for Dynamic Bond Evolution in Single-Atom Pt/C₃N₄ Catalysts. Angewandte Chemie International Edition. 59(15):6224–6229. https://doi.org/10.1002/anie.201915774.
Fu J, Yu J, Jiang C, Cheng B (2018) g-C₃N₄-Based Heterostructured Photocatalysts. Advanced Energy Materials 8:1–31. https://doi.org/10.1002/aenm.201701503
Fang ZL, Rong HF, Ya ZL, Qi P (2015) In-situ synthesis of CdS/g-C₃N₄ hybrid nanocomposites with enhanced visible photocatalytic activity. Journal of Materials Science 50:3057–3064. https://doi.org/10.1007/s10853-015-8865-8
Guo F, Wang L, Sun H, Li M, Shi W. (2020) High-efficiency photocatalytic water splitting by a N-doped porous g-C₃N₄ nanosheet polymer photocatalyst derived from urea and: N, N -dimethylformamide. Inorganic Chemistry Frontiers 7:1770–1779. https://doi.org/10.1039/d0qi00117a
Chen P, Chen L, Ge S, Zhang W, Wu M, Xing P, Rotamond T.B, Lin H, Wu Y, He Y. (2020) Microwave heating preparation of phosphorus doped g-C₃N₄ and its enhanced performance for photocatalytic H₂ evolution in the help of Ag₃PO₄ nanoparticles. International Journal of Hydrogen Energy 45:14354–14367. https://doi.org/10.1016/j.ijhydene.2020.03.169
Liu J, Yan XT, Qin X Sen, Wu S-J, Zhao H, Yu B-W, Chen L-H, Li Y, Su B-L. (2020) Light-assisted preparation of heterostructured g-C₃N₄/ZnO nanorods arrays for enhanced photocatalytic hydrogen performance. Catalysis Today 355:932–936. https://doi.org/10.1016/j.cattod.2019.02.028
Moharrami P, Motamedi E. (2020) Application of cellulose nanocrystals prepared from agricultural wastes for synthesis of starch-based hydrogel nanocomposites: efficient and selective nano-adsorbent for removal of cationic dyes from water, Bioresour. Technol. 313, 123661, https://doi.org/10.1016/j. biortech.2020.123661.
Wang H, Li J, Ding N, Zeng X, Tang X, Sun Y, Lei T, Lin L. (2020) Eco-friendly polymer nanocomposite hydrogel enhanced by cellulose nanocrystal and graphitic-like carbon nitride nanosheet. Chemical Engineering Journal 386:124021. https://doi.org/10.1016/j.cej.2020.124021
Jiang N, Lyu L, Yu G, Zhang L, Hu C. (2018) A dual-reaction-center Fenton-like process on-CN-Cu linkage between copper oxides and defect-containing g-C₃N₄ for efficient removal of organic pollutants. Journal of Materials Chemistry A 6:17819–17828. https://doi.org/10.1039/c8ta04873h
Amutha T, Rameshbabu M, Muthupandi S, Prabha K. (2021) Materials Today: Proceedings Theoretical comparison of lattice parameter and particle size determination of pure tin oxide nanoparticles from powder X-ray diffraction. Materials Today: Proceedings. https://doi.org/10.1016/j.matpr.2021.08.044
Das R, Sarkar S (2015) X-ray diffraction analysis of synthesized silver nanohexagon for the study of their mechanical properties. Materials Chemistry and Physics 167:97–102. https://doi.org/10.1016/j.matchemphys.2015.10.015
Wang W, An T, Li G, Xia D, Zhao H, Yu J.C, Wong P.K. (2017) Earth-abundant Ni₂P/g-C₃N₄ lamellar nanohydrids for enhanced photocatalytic hydrogen evolution and bacterial inactivation under visible light irradiation. Applied Catalysis B: Environmental 217:570–580. https://doi.org/10.1016/j.apcatb.2017.06.027
Zhang Y, Wang G, Jin Z. (2019) An orderly assembled g-C₃N₄, rGO and Ni2P photocatalyst for efficient hydrogen evolution. International Journal of Hydrogen Energy 44:10316–10327. https://doi.org/10.1016/j.ijhydene.2019.03.006
Wang W, Fang J, Shao S, Lai M, Lu C. (2017) Compact and uniform TiO₂@g-C₃N₄ core-shell quantum heterojunction for photocatalytic degradation of tetracycline antibiotics. Applied Catalysis B: Environmental 217:57–64. https://doi.org/10.1016/j.apcatb.2017.05.037
ï»¿Gopal J, Elumalai G, Tajuddin A.A.H, Ito Y, Vajiravelu S, Ravikumar D.(2022). Recyclable Clay-Supported Heteropolyacid Catalysts for Complete Glycolysis and Aminolysis of Post-consumer PET Beverage Bottles. J. Polym. Environ. 30:2614–2630. https://doi.org/10.1007/s10924-022-02386-5
ï»¿Jeya G, Ilbeygi H, Radhakrishnan D, Sivamurugan V. (2017). Glycolysis of Post-Consumer Poly(ethylene terephthalate) Wastes Using Al, Fe and Zn Exchanged Kaolin Catalysts with Lewis Acidity. Adv. Porous Mater. 5:128–136. https://doi.org/10.1166/apm.2017.1141
Jeya G, Anbarasu M, Dhanalakshmi R, Vinitha V, Sivamurugan V. (2020). Depolymerization of Poly(ethylene terephthalate) Wastes through Glycolysis using Lewis Acidic Bentonite Catalysts. Asian J. Chem. 32:187–191. https://doi.org/10.14233/ajchem.2020.22387

Scheme 1 is available in the Supplementary Files section

No competing interests reported.

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Graphical abstract
Scheme1.png
Scheme 1 Depolymerized PES textile waste on glycolysis and aminolysis final Products BHET & BHETA

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published 28 Jan, 2024

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Valorization of PES textile waste through glycolysis and aminolysis using bimetallic ZnO and carbon nitride nanocomposites

Status:

Journal Publication

Version 1

Abstract

Figures

Highlights

1 Introduction

2 Experimental

2.1 Materials

2.2 Synthesis of Catalyst

2.2.1 Pure graphene carbon Nitride (g-C3N4) Catalyst

2.2.2 Synthesis of In- and Sb-doped ZnO nanoparticles

2.2.3 Preparation of the g-carbon nitride-doped bimetallic ZnO catalyst

2.3 Catalytic activity of g-C3N4 doped with indium and antimony-doped ZnO

2.3.1 Aminolysis of PES textile waste under microwave irradiation

2.3.2 Glycolysis of PES textile waste under microwave irradiation

2.4 Characterization of catalyst and depolymerized products

2.4.1 XRD

2.4.2 FT- IR

2.4.3 UV‒Vis

2.4.4 SEM Analysis

3 Results and Discussion

3.1 Characterisation of nanocomposites

3.1.1 XRD Analysis

3.1.2 Absorption maxima and optical bandgap

3.1.3 FT-IR spectroscopy

3.1.4 SEM with EDS analysis

3.2 Optimization of aminolysis and glycolysis of PES textile wastes

3.2.1 Effect of Catalyst Activity

3.2.2 Effect of Microwave power

3.2.3 MW irradiation time

3.2.4 Effect of PET to Solvent ratio

3.2.5 Catalyst Recycling Studies

3.3 Decolorization of pure polyester (PES) color threads

3.4 Spectral characterization of BHETA and BHET

3.4.1 FT-IR spectrum analysis BHETA and BHET

3.4.2 1H and 13C NMR Spectrum of BHETA

3.4.3 1H and 13C NMR Spectrum of BHET

3.4.3 Mass spectrum of BHETA and BHET

4 Conclusions

Declarations

References

Scheme 1

Additional Declarations

Supplementary Files

Status:

Journal Publication

Version 1

2.2.1 Pure graphene carbon Nitride (g-C₃N₄) Catalyst

2.3 Catalytic activity of g-C₃N₄ doped with indium and antimony-doped ZnO

3.4.2 ¹H and ¹³C NMR Spectrum of BHETA

3.4.3 ¹H and ¹³C NMR Spectrum of BHET