Novel Methodology of Chitosan-Salicaldehdye Polymers: Synthesis, Charactrization, and application in NH3 sensing

doi:10.21203/rs.3.rs-3321200/v1

Chitosan-salicylaldehyde polymer derivatives were formed via chitosan modification. These polymers were synthesized through inclusion with β-cylcodextrine and doping with ZnO nanoparticles to give pseudopolyrotaxane and Chs-Sal/ZnO NPs composite, respectively. Additionally, the complicated polymer (Chs-Sal/ β-CD/ZnO NPs) was prepared via insertion of generated composite (Chs-Sal/ZnO NPs) through β-cyclodextrin ring. The structural and morphological characterizations of the novel synthesized derivatives were confirmed by utilizing FT-IR, XRD and SEM analysis, respectively. Also, the optical properties and thermal gravimetric analysis of the synthesized polymers were explored. The released results confirmed that using β-CD or ZnO NPs for modification of polymer (chs-sal) dramatically enhanced the thermal stability and optical features of the synthesized polymers. Investigations on the NH₃-sensing properties of Chs-Sal/β-CD/ZnO NPs composite were carried out at concentrations down to 10 ppm at RT. It was found that modification by β-CD and doping with ZnO NPs improves effectively the NH₃-sensing response of Chs-Sal and exhibited good selectivity and good response-recovery time at RT.

Chitosan

Cyclodextrin

ZnO NPs

pseudopolyrotaxane

salicylaldehyde

NH3 sensor.

Chs-Sal polymer derivatives were formed through chitosan-salicaldehyde polymer modification.
Chs-Sal polymer derivatives were estimated by XRD, FTIR and SEM analysis.
Modification of Chs- Sal polymer through inclusion into β-CDs and doping with ZnO NPs had a potential application prospect in NH₃ monitoring.

Polymers have been emerged as inevitable in our daily lives because of their many applications in various fields such as medical [1,2], automobile [3], aerospace [4], electronics [5], packaging [6], food [7], photophysics [8] and ferro-electrics [9]. It is well known that synthetic polymers are harmful to the environment due to their non-degradation [10]. Therefore, researchers tend to replace these synthetic polymers with biopolymers such as cellulose, chitin, chitosan and poly peptides [11–14]. However, chitosan is superior to the other bio-polymers due to its crystallinity, nitrogen richness, hydrophilicity and high viscosity ionic conductivity [15]. Chitosan is extracted from the shells of shrimp and other easily crustaceans [16].The amino group of chitosan has received considerable interest as it forms the corresponding Schiff base (SB) [17–20]. This imino group has many applications as pharmaceutical agents, sensors, key intermediates for biochemical reactions, corrosion inhibitors, sorbents and organo-catalysts [21–23]. Finally, modification of chitosan through chemical, radiation, enzymatic and physical methods can produce a biopolymer that has more tendencies to interact with other components [24]. Chitosan has also different active groups such as primary and secondary hydroxyl group in its monomer, so it can be chemically modified by interaction with other components, such as metal ions, organic compounds [25].

Cyclodextrine (CD) is well known type of macrocyclic compound obtained by intermolecular connection of D-(+)-glucopyranosyl units [26]. CDs are class of oligosaccharides with an important role in the pharmaceutical research and global market, which are formed by starch under the function of amylase enzyme [27]. It is predominantly divided into three products: α-, β- and γ-CDs, which are composed of 6, 7 and 8 glucose units, respectively. In general, the most used is β-CD, because it has a low production cost and moderate molecular void space, which makes more suitable for various fields [28].

Interestingly, ammonia is used in various fields such as food, industrial, cleaning, and chemical manufacturing [29]. Moreover, ammonia has also been utilized as a key signal in the detection of conditions including diabetes, renal illness, malignant tumors, and lung cancer since it is a metabolite in human life [30]. Despite its use, NH₃ is a poisonous gas that is detrimental to human health and colorless and it also has a strong stench [31]. For instance, exposure to 25 ppm of NH₃ might irritate the skin, eyes, and lungs in individuals [32]. Inorganic compounds (metal-oxides) and organic materials (conducting polymer) have been the subject of studies on NH₃ gas sensors [33]. The metal-oxides-based gas sensors may have a high sensing response and a low detection limit of concentration.

We study the modification of chitosan-salicylaldehyde (Chs- Sal) polymer through inclusion into β-CDs and doping with ZnO nanoparticles (NPs) to give (Chs-Sal/β-CD)pseudopolyrotaxaneand Chs-Sal/ ZnO NPs composite. Moreover, modify Chs- Sal polymer through insertion into β-CDs and doping with ZnO nanoparticles (NPs) in one pot reaction to afford (Chs-Sal/β-CD/ZnO NPs) pseudopolyrotaxane composite in a cheap, simple and eco-friendly route. The modified polymers exhibit elevated crystallinity, wide optical properties and thermal stability making them suitable for wide applications such as toxic vapor and gas sensing.

2.1. Materials

Chitosan with deacetylation degree above 85%, salicylaldehyde and β-CD were purchased from Merck co., Germany. ZnO NPs (purity over 97%, >50 nm), glacial acetic acid, dimethylformamide (DMF) were supplied from Aldrich, Milwaukee, Wisconsin, USA. All chemicals and solvents were used herein are purchased from Sigma-Aldrich with analytical grade and are used as received without futher purification.

2.2. Synthesis of Chs-Sal polymer

Chitosan powder (1.0 g) in 50 ml of (1% v/v) glacial acetic acid was stirred at room temperature then added a solution of salicylaldehyde (0.40 g in 10 ml MeOH) at room temperature for 6 h then the temperature was raised to 100 °C for 1 h, Scheme 1. The used solvent was evaporated at room temperature to give the Chs-Sal polymer as a yellow powder.

2. 3. Synthesis of pseudopolyrotaxane (Chs-Sal/ β-CD)

A mixture of Chs-Sal polymer (1.0 g) and β-CD (2.0 g) in DMF (25 ml) was stirred at room temperature for 24 h, Scheme 2. The obtained precipitate dried at room temperature to afford Chs-Sal/ β-CD as a pale-yellow powder.

2. 4. Synthesis of Chs-Sal/ZnO NPs composite

A mixture of Chs-Sal polymer (1.0 g) and ZnO NPs (0.10 g) in DMF (25 ml) was stirred at room temperature for 30 h, Scheme 3. The formed hydrogel was poured into a Petri dish and dried at room temperature to afford Chs-Sal/ ZnO NPs as green crystals.

2. 5. Synthesis of Chs-Sal/ β-CD /ZnO NPs composite

A mixture of Chs-Sal polymer (1.0 g), ZnO NPs (0.10 g) in DMF (25 ml) was stirred at room temperature for 6 h. Then, β-CD (2.0 g) in DMF (25 ml) was added with stirring at room temperature for 48 h, Scheme 4. The formed hydrogel was poured into a Petri dish and dried at room temperature to afford Chs-Sal/ β-CD /ZnO NPs composite as a pale-yellow crystal.

2. 6. Characterizations

2. 6. 1. Fourier-transformation infrared (FTIR)

The structure of the produced derivatives was studied by using FTIR spectroscopy at room temperature (infrared spectrometer: Jasco Model 4100 – Japan) in the wavenumber region of 4000 – 400 cm¹.

2. 6. 2. X-ray diffraction (XRD)

The crystallite size and phase structure of the polymers were determined by XRD measurements taken at room temperature with a powder diffractometer (Brucker D8 Advance, Germany) equipped with a Cu K radiation source, = 1.5406 and 2 in the range (5–80°).

2. 6. 3. Scanning electron microscope (SEM)

SEM (JEOL SEM model JSM – 5500 – Japan) with accelerated voltage 20 kV was used to study the morphological structures of the produced derivatives.

2. 6. 4. Thermogravimetric analysis (TGA)

The thermal stability of the synthesized derivatives was measured using a TGA (SDT Q600 V20.9 Build 20) with a 5 °C/min heating rate up to 400 °C and a 5 ml/min nitrogen gas flow. A data collecting and handling mechanism is built into the thermal analyzer (TA-50WSI).

2. 6. 5. UV–visible spectroscopy

The optical characteristics of the produced polymers were determined using UV–visible spectroscopy. The UV–visible spectra were obtained by using a UV–visible spectrophotometer (PG Instruments, model T80, UK) and quartz cells with a path length of 1 cm with wavelengths ranging from 200 to 800 nm. To modify the baseline, DMF was utilized as a blank.

2.7. Gas sensing studies

The gas-sensing performance of the prepared composites was achieved using a homemade static system consists of a 5 L glass chamber and a laptop interfaced digital multimeter for signal acquisition [34,35]. The sensor was fabricated by painting the composite paste on interdigital electrode interdigitated electrodes (5 cm×4 cm×2 cm) and dries at 45 ^oC for 24 h.

Different volumes of volatile liquids were injected into the bottle using a syringe to obtain the corresponding concentrations. The sensor response was calculated from the relation , where R_a and R_g represent resistances of the sensor in the air and in the presence of tested gas, respectively. The response time and recovery time are defined as the elapsed time to reach 90% of the final equilibrium value [36].

3. 1. SEM analysis

Figure 1 show the SEM images the surface morphology of chitosan, β-CD, ZnO NPs, and the generated chitosan polymers ( Fig. 1 a-g). These images show apparent differences between them, and the surface appearances were changed upon reaction as compared to fibrous nature of chitosan’s surface. The Chs-Sal polymer was appeared as rough amorphous slides (Fig. 1-b). Additionally, the surface morphology of β-CD and pseudopolyrotaxane polymer showed higher difference between them due to the insertion of Chs- Sal polymer into the β-CD (Fig. 1-d). Pseudopolyrotaxane polymer showed a scaly and slightly rough structure with bigger random particle crystal size. SEM images of Chs-Sal/ZnO NPs composite showed smooth slides without pores surface. The pores of Chs-Sal polymer considered as a particle sink to get ZnO NPs inside it for form the soft surface of composite (Fig. 1-f). The surface morphology of pseudopolyrotaxane polymer was changed in Chs-Sal/ β-CD/ ZnO NPs composite (Fig. 1-g). It has become uneven and aggregated in Chs-Sal/ β-CD/ ZnO NPs composite.

3. 2. XRD analysis

Analyze the phase structure and its crystallite size of chitosan, Chs- Sal polymer, β-CD, pseudopolyrotaxane polymer, ZnO NPs, Chs-Sal/ZnO NPs, Chs-Sal/ β-CD/ ZnO NPs composite, XRD analysis has been accomplished (Fig. 2 and 3). XRD spectra were recorded at 25 ^ºC in the range 5^º−80^º. The characteristic diffraction peaks of chitosan were observed at 2θ = 8.6^º and 20^ºconfirming its semi-crystalline nature [37, 38]. XRD analysis showed the formation of Schiff base (Chs- Sal polymer) via the changing of amino group nature. Moreover, the difference in the crystal size and crystallinity of chitosan as indicated by disappearance peaks in 16.4^º, 33.6^º and appearance of a slight peak in 13.8^º. Additionally, the crystallinity values of Chitosan and the formed Chs-Sal polymer showed 57.7 and 50.6 %, respectively. The crystallinity value of Chs-Sal decreased due to the formation of Schiff base and cleavage of hydrogen bonds [39]. The XRD pattern of pseudopolyrotaxane polymer showed sharp diffraction angle at 14.2^º and the crystallinity value was 48.3% and the crystal size increased compared to Chs-Sal polymer (crystal size values of Chs-Sal and pseudopolyrotaxane polymer were 2.4 and 3.2 nm, respectively. After addition of ZnO NPs to the Chs-Sal polymer gave a different pattern in XRD analysis. A broad peak in the blind polymer became a broader peak with less intensity and some sharp peaks appeared at 15^º, 17^º, and 29.9 º. Moreover, the crystal size of Chs-Sal/ZnO NPs (3.8 nm) increased on the cost of crystallinity value (46.1%), this difference indicates the interaction between the ZnO NPs and Chs-Sal polymer. Finally, Chs-Sal/ β-CD/ ZnO NPs composite XRD result showed broad peaks at 13.3^º, 13.7^º, 14.2^º, 14.6^º, 17.6^º, 18.2^º, higher crystal size 5.78 nm and lower crystallinity value 45%.

3. 3. Fourier-transform infrared spectroscopy (FT-IR)

FT-IR spectra were used to confirm the formation of our components. Fig 4 showed the difference between the Chs and Chs-Sal polymer as a Schiff base. The -OH group characteristic peak in chitosan appeared at 3334 cm^-1, which appears superimposed to the N-H stretching band and the hydrocarbon bond C-H appeared at 2978 cm^-1. In addition to the peaks of -C=O amide and –NH₂ were observed at 1657 cm^-1 and 1598 cm^-1. The spectrum of Schiff base polymer showed C=N band at 1631 cm^-1, such results confirmed the Chs-Sal polymer formation. Moreover, the stretching and bending vibration peaks of C-C bonds on the aromatic ring of the aldehyde and the stretching vibration peak of -C-O of Sal appeared at 1490, 820 and 1250 cm^-1, respectively [40-42]. For clearance the characteristic band of salicaldehyde in the region 1660-1730 cm^-1has not appeared in Schiff base spectrum indicating that there is no traceable residue of free Sal. The differences between absorbance bands of chitosan and Chs-Sal polymer are summarized in Table 1.

Table 1. FT-IR changes of pure Chs and Chs-Sal polymer

Functional Groups	Wave number, cm¹
	Chs	Chs-Sal	∆ν
ν[OH, NH] symmetric	3343	3373	-30
ν [ CH aliphatic]	2978	2960	+18
ν [ C-O]	1657	1649	+8
ν [ C-N]	-	1631	-
ν [ CH₂-OH]	1378	1370	+7
ν [ C-O-C]	1068	1072	-4

ν= ν (Chs-Sal polymer) – ν(Chs).

We noticed that the absorption band of the hydroxyl group is slightly higher and less intensity than the β-CD sample (Fig. 4). Also, the ν[OH] symmetric stretching was shifted to higher frequency and ν[CH-aliphatic] was shifted to lower frequency compared to those in β-CD. Furthermore, the ν[C–O–C] and ν[CH₂-O] bending vibrations were shifted to lower frequencies at 1027 and 1158 cm^-1, respectively. These results confirmed the formation of pseudopolyrotaxane polymer through the reaction of Chs-Sal polymer with β-CD. This result can be explained as follow, the insertion of the Chs-Sal chain through the electron rich cavity of the cyclodextrin rings lead to increasing the frequencies [43]. On the other hand, the decrease in frequencies is due to the formation of Vander Waals forces and hydrogen bonds between the hydroxyl groups of β-CDs and carbonyl groups of chitosan and salicylaldehyde molecules as well as the hydrogen bond between the adjacent β-CDs, Fig 4. The differences between absorbance bands of pure β-CD, Chs-Sal polymer and pseudopolyrotaxane polymer are showed in Table 2.

Table 2. FT-IR changes of β-CD, Chs-Sal polymer, and pseudopolyrotaxane polymer.

Functional groups			Wave number, cm¹
	∆ν₁	Chs-Sal polymer		pseudopolyrotaxane	β-CD	∆ν₂
ν[OH, NH] symmetric	+23	3373		3396	3389	+7
ν [ CH aliphatic]	-60	2960		2900	2925	-25
ν [ C-O]	+19	1649		1668	-	-
ν [ CH₂-OH]	-22	1370		1158	1159	-1
ν [ C-O-C]	-45	1072		1027	1028	-1

∆ν₁ = ν(pseudopolyrotaxane) –ν(Chs-Sal polymer), ∆ν₂= ν(pseudopolyrotaxane) –ν( β-CD).

The FT-IR spectrum of the Chs-Sal/ZnO NPs polymer in Fig 5, showed a broad absorption band at 3408 cm^-1 corresponds to the stretching vibrations of hydroxyl (OH) groups. The absorption band at 2945 cm^-1 is attributed to symmetric stretching of aliphatic C–H groups of Chs in polymer blend [44],which is markedly shifted and decreased in intensity (2930 cm⁻¹) upon doping of ZnO NPs. The absorption band at 1660 cm^-1 assigned to free C=O stretching vibration [45]. The absorption bands at 1560 and 1413 cm^-1 corresponds to the polymer (C=N) group [46] bending and the stretching vibration of (CH₂-OH) group, respectively, were shifted towards higher wave numbers and decreased in their intensities, because of the interaction between the polymer blend chains and the ZnO NPs [47]. The band at 1073 cm^-1 is attributed to C–O–C stretching became less intense and shifted to lower wavenumber. The differences between absorption bands of Chs-Sal polymer and Chs-Sal polymer doped with ZnO NPs are summarized in Table 3. These changes (shift and decrease in the intensity) indicated the strong interaction between these functional groups in the polymer blend and ZnO NPs. The absorption band at 675 cm^-1 is appeared due to the stretching mode of the amide groups attached to zinc oxide NPs, Fig. 5 [48, 49].

Table 3. FT-IR changes of Chs-Sal polymer, Chs-Sal/ ZnO NPs composite and ZnO NPs .

Functional groups			Wave number, cm¹
	∆ν₁	Chs-Sal polymer		Chs-Sal/ ZnO NPs	ZnO NPs	∆ν₂
ν[OH, NH] symmetric	+107	3373		3480	3333	+147
ν [ CH aliphatic]	-30	2960		2930	-	-
ν [ C-O] ν [NH-bending]	-11 +50	1649 1570		1660 1620	- 1553	- +67
ν [ CH₂-OH]	+43	1370		1413	1393	+20
ν [ C-O-C]	+1	1072		1073	1090	-13

∆ν₁ = ν(Chs-Sal/ ZnO NPs) –ν(Chs-Sal polymer), ∆ν₂ = ν(Chs-Sal/ ZnO NPs)- ν(ZnO NPs).

Fig 6 showed the difference between Chs-Sal polymer, Chs-Sal/ ZnO NPs composite, Chs-Sal/ β-CD and Chs-Sal/ β-CD /ZnO NPs composite. The FT-IR spectrum of the Chs-Sal/ β-CD /ZnO NPs composite showed a broad absorption band of –OH group at 3375cm^-1 with increasing of intensity compared to the last polymers. The absorption band of aliphatic C–H groups at 2927 cm^-1, which is markedly shifted and increased in intensity. The absorption band at 1663 cm^-1 assigned to free C=O stretching vibration, and C-N group appeared at 1663 cm^-1 with high intensity. The absorption bands at 1158 and 1028 cm^-1correspond to the stretching vibration of (CH₂–OH) group and C–O–C stretching became more intense and shifted to lower wavenumber. These changes (shift and increase in the intensity) indicate the strong interaction between these functional groups in the polymer blend of pseudopolyrotaxane and ZnO NPs. The absorption band at 756 cm^-1 appeared due to the stretching mode of the amide groups attached to zinc oxide NPs. The differences between absorption bands of Chs-Sal/ ZnO NPs polymer, Chs-Sal/ β-CD polymer and Chs-Sal/ β-CD/ZnO NPs polymer are summarized in Table 4.

Table 4. FT-IR changes of Chs-Sal/ ZnO NPs polymer, Chs-Sal/ β-CD polymer and Chs-Sal/ β-CD/ZnO NPs polymer.

Functional groups	Wave number, cm¹
	∆ν₁	Pseudopolyrotaxane	Chs-Sal/ β-CD/ ZnO NPs	Chs-Sal/ ZnO NPs	∆ν₂
ν[OH, NH] symmetric	-21	3396	3375	3480	-105
ν [ CH aliphatic]	+27	2900	2927	2930	-3
ν [ C-O]	-5	1668	1663	1660	+3
ν [ CH₂-OH]	-2	1158	1156	1413	-257
ν [ C-O-C]	+1	1027	1028	1073	-45

∆ν₁ = ν(Chs-Sal/ β-CD/ ZnO NPs) –ν(pseudopolyrotaxane), ∆ν2 = ν(Chs-Sal/ β-CD/ ZnO NPs) –ν(Chs-Sal/ ZnO NPs).

3. 4. Optical properties

UV-visible spectroscopy of Chs-Sal polymer, Chs-Sal/ZnO NPs composite, Chs-Sal/ β-CD and Chs-Sal/ β-CD/ZnO NPs composite were recorded in the range of 200–800 nm at 25 °C (Fig. 7). The UV-visible spectrum of Chs-Sal polymer showed a broad peak at the region 327–360 nm due to the presence of π bond(–N=CH–). Interestingly, modification of Chs-Sal polymer with β-CD and ZnO NPs exhibited slight blue shifts in the characteristic peak, from 360 to 340 and 356 nm, respectively. Also, in the case of addition of β-CD and ZnO NPs into Chs-Sal as a one pot reaction gave sharp peak in 439 nm. These data approved the formation of Chs-Sal/ZnO NPs composite, Chs-Sal/ β-CD and Chs-Sal/ β-CD/ZnO NPs composite. Additionally, the energy gap energy of the prepared polymers was calculated depending on the UV-visible absorption spectra according to Tauc's formula. The values of Eg for Chs-Sal polymer,Chs-Sal/ β-CD,Chs-Sal/ZnO NPs composite and Chs-Sal/ β-CD/ZnO NPs composite were 4.4, 3.55, 2.65 and 3.11 eV, respectively.

3.5. Thermal analysis

Thermogravimetric analysis was carried out to study the thermal stability of the prepared polymers and their resistance to heat. Fig. 8 shows the TGA curves of Chs-Sal,Chs-Sal/ZnO NPs composite, Chs-Sal/ β-CD and Chs-Sal/ β-CD/ZnO NPs composite. Generally, it is clear from this Fig that the thermal stability decreased in case of Chs-Sal/ β-CD composite compared with Chs-Sal polymer whereas the weight loss at 350°C is 67 % and 52%, respectively. In addition, the incorporation of ZnO NPs was slightly increased the heat resistance of the produced Chs-Sal/ZnOcomposite (the weight loss at 350°C is 47 %). On the other hand, the thermal stability of Chs-Sal/ β-CD/ZnO NPs composite increased 55 % at the same temperature compared with Chs-Sal/ β-CD, due to the addition of ZnO NPs increased the stability of polymer. Depending on the results in Fig. 8, the order of thermal stability of the four samples is Chs-Sal/ β-CD/ZnO NPs ˃ Chs-Sal/ ZnO NPs Chs-Sal ˃ Chs-Sal/ β-CD ˃ Chs-Sal.

3.6. Gas sensing properties

Fig. 9 (a, b) shows the response of the polymer composite as sensor towards NH₃ various concentrations at room temperature. The Chs-Sal/ β-CD/ZnO NPs composite sensor exhibited high sensing characteristics toward NH₃ down to 10 ppm concentration. It was observed that the sensor response was increased by increasing NH₃ concentration, and recovered after purging the chamber with air, indicating reversible response characteristics of the composite. Due to the presence of ZnO NPs on the exterior surface of β-CD in the Chs-Sal/ β-CD/ZnO NPs composite, β-CD enhances the dispersibility and surface area of ZnO NPs which results in the presence of more reactive sites onto the ZnO NPs surface which increases the amount of the adsorbed gas and the response as well [50,51]. In addition, the hydrophilic nature of the exterior surface of β-CD due to the distribution of hydroxyl groups may also participates in the adsorption of NH₃ molecules [52,53]. Moreover, many vapor channels in the cavities of β-CD in addition to the inclusion of Ch-Sal-ZnO into these cavities may enhance the sensor response of Chs-Sal/ β-CD/ZnO NPs composite [54]. Furthermore, the inner cavity of β-CD may occupied by traces of water vapor from the atmospheric air which may also interact with NH₃ vapor [55,56]. The sensor response and recovery times were 650 s and 350 s, respectively, indicating that Chs-Sal/ β-CD/ZnO NPs composite is suitable for gas sensing applications. Besides, the selectivity of the Chs-Sal/ β-CD/ZnO NPs composite sensor has also been studied at room temperature upon exposure to various 100 ppm gases/vapors (NH₃, chloroform, ethanol, and methanol) as depicted in Fig. 9c. the results indicating that the Chs-Sal/ β-CD/ZnO NPs composite sensor exhibits the highest response when exposure to 100 ppm NH₃suggesting that the Chs-Sal/ β-CD/ZnO NPs composite is has excellent selectivity in NH₃-monitoring application. Fig. 9(d) shows the response comparison of Chs-Sal , Chs-Sal/β-CD, Chs-Sal/ZnO NPs, and Chs-Sal/β-CD/ZnO NPs composite as sensors to 100 ppm of NH₃ at RT. The obtained observations indicated that Chs-Sal/β-CD/ZnO NPs composite exhibited improved NH₃ sensing response compared to other polymers.

Stirring at room temperature of chitosan polymer as amine with salicaldehyde as a carbonyl component afforded Chs-Sal polymer. The obtained Chs-Sal was added to β-CD to form pseudopolyrotaxane inclusion complex, and doped with ZnO NPs to produce the corresponding composite in adequate and simple with low cost effective and an eco-friendly environmentally. Chitosan, salicaldehyde, ZnO NPs and β-CD were reacted as one pot reaction to form Chs-Sal/ β-CD/ZnO NPs polymer. These derivatives were confirmed by FT-IR and XRD analyses, while SEM analysis indicated remarkable morphological changes between them. UV-visible results confirmed the improvement of the optical properties of the prepared samples, as well as the energy band gap values. The thermal stability of Chs-Sal polymer was enhanced by doping with ZnO NPs. Chs-Sal/ZnO NPs increased the inhibition efficiency (91.16 %) in comparison to Chs-Sal/ -CD/ZnO NPs due to the small particle crystal size produces an uneven and aggregated layer. Gas sensing results showed that the modification of chitosan-salicylaldehyde polymer through inclusion into β-CDs and doping with ZnO nanoparticles (NPs) had a potential application prospect in NH₃ monitoring.

Author contribution

The experiments were carried out by Ahmed G. Taha and Ahmed M. Saeed. The manuscript was written by all the authors. All authors discussed the results and commented on the manuscript.

Funding Open access funding provided by The Science, Technology & Innovation Funding Authority (STDF) in cooperation with The Egyptian Knowledge Bank (EKB).

Data availability All data is contained within the manuscript.

Ethical approval Not applicable

Competing of interest The authors declare no competing interests.

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Schemes 1 to 4 are available in the Supplementary Files section.

No competing interests reported.

Scheme1.jpg
Scheme 1. Synthesis of Chs-Sal polymer
Scheme2.jpg
Scheme 2. Synthesis of Chs-Sal/ β-CD composite
Scheme3.jpg
Scheme 3. Synthesis of Chs-Sal/ZnO NPs composite
Scheme4.jpg
Scheme 4. Synthesis of Chs-Sal/ β-CD /ZnO NPs composite

Novel Methodology of Chitosan-Salicaldehdye Polymers: Synthesis, Charactrization, and application in NH₃ sensing

Status:

Version 1

Abstract

Figures

Highlights

1. Introduction

2. Materials and methods

3. Results and discussion

Conclusion

Declarations

References

Schemes

Additional Declarations

Supplementary Files

Status:

Version 1