Tungsten oxide nanostructures peculiarity and photocatalytic activity for the efficient elimination of the organic pollutant

The WO3 nanostructures were synthesized by a simple hydrothermal route in the presence of C14TAB and gemini-based twin-tail surfactant. The impact of using these special shape and size directing agents for the synthesis of nanostructures was observed in the form of different shapes and sizes. The WO3 web of chains type nanostructure was obtained using C14TAB in comparison to the cube-shaped nanoparticles through twin-tail surfactant. On contrary, the twin-tail surfactant provides sustainable and controlled growth of cube shape nanoparticles of size ~ 15 nm nearly half of the size ~ 35 nm obtained using conventional surfactant C14TAB, respectively. For the detailed structural features, the Williamson–Hall analysis method was implemented to find out the crystalline size and lattice strain of the prepared nanostructures. Owing to the strong quantum confinement effect, the WO3 cube-shaped nanoparticles with an optical band gap of 2.69 eV of the prepared nanoparticles showed excellent photocatalytic efficacy toward organic pollutant (fast green FCF) compared to the web of chain nanostructures with an optical band gap of 2.66 eV. The ability of the prepared systems to decompose the organic pollutant (fast green FCF) in water was tested under visible light irradiations. The percentage degradation was found to be 94% and 86% for WO3 cube-shaped nanoparticles and WO3 web of chains, respectively. The simplicity of the fabrication method and the high photocatalytic performance of the systems can be promising in environmental applications to treat water pollution.


Introduction
Nowadays, the engineered nanostructures and their exceptional surface features such as high surface-to-volume ratio, multi-functional possibility, and illustrious surface reactivity have achieved great promises for a variety of consumers and industrial applications, by making the materials lighter, more robust, and more proficient in comparison to their bulk equivalents (Hou et al. 2018). In contrast to the traditional semiconductors (Si, Ge, etc. with a band gap ‹ 2 eV), metal oxides are recognized as wide bandgap (›2 eV) semiconductors with electron transition energy in the range of ultraviolet and visible light which results in a solution for the inadequacies with the traditional semiconductors (Park et al. 2017;Guo et al. 2019). Furthermore, wide band-gap semiconductors materials are also stable at high temperatures, can perform efficiently under high currents and voltage, and show higher carrier density and mobility (Chaves et al. 2020). Because of the wide band gap of most of the metal oxides, they are also comparable to the electrode potential of various significant reactions, such as the oxidation of organic molecules, splitting of water to produce both hydrogen and oxygen, reduction of CO 2 , and degradation of the various pollutants and dyes (Singh et al. 2020;Jamwal et al. 2022).
In recent decades, tungsten oxide nanostructures have shown remarkable applications in many fields such as solar cells, nanolasers, gas sensors (Cao et al. 2016), electron Responsible Editor: Sami Rtimi field emitters (Lin et al. 2019), light-emitting diodes (LEDs), electrochromic films , and as a photocatalyst. Tungsten oxide is an exclusive semiconductor material with a characteristic wide and direct band gap of 2.6 to 3.7 eV for various structures, which can be affected by particle size and shape of the material. The controlled size and shapes of the synthesized materials have been approved as important steps for the exploration of the material for use in photocatalytic, electrocatalytic, thermochromic, photochromic devices, etc. (Yang et al. 2019). In this respect, the use of surfactants in the synthesis method can lead to nanomaterials with controlled size and morphology with desired properties. The unique properties of the special type of twin-tail surfactants, i.e., gemini surfactants encouraged us to use these molecules for the synthesis of tungsten oxide nanoparticles. In comparison with conventional surfactants , gemini surfactants have distinctive features such as their very low critical micelle concentration (cmc), good water solubility, greater efficacy for reducing the surface tension of water, and low Kraft point ). Owing to these special features of twin-tail (gemini) surfactants, they adsorb on the low crystal facets selectively and reduce their participation in the nucleation process so that explicit crystal growth takes place at uncapped or poorly capped high energy crystal facets to achieve preferred morphologies. Conferring to former studies, twin-tail surfactants significantly influenced the size and shape of the nanostructures and subsequently their applications (Bakshi et al. 2007(Bakshi et al. , 2010. On the other side, some studies are limited to use the conventional capping agents (Mirtaheri et al. 2017;Aliasghari et al. 2020;Govindaraj et al. 2020) with high cmc, low water solubility, and less efficacy for the reduction of surface tension, and predominantly the effect of gemini surfactants on the size and shape of metal oxide nanoparticles has hardly been investigated. Therefore, additional investigations are essential to elucidate the impact of twin-tail surfactants on structure of metal oxides.
Organic dyes are one of the foremost leading cause of water pollution, which results in serious environment problems and risk to human health. The different commercial dyes are categorized by sturdy structural and color stability owing to their high degree of aromaticity. Therefore, these dyes need to be treated/removed before their discharge into fresh water streams to evade their hazardous influence (Qamar et al. 2020;Nagajyothi et al. 2020). In recent past, 94 to 99% photodegradation of different organic dyes such as methylene blue (Sagadevan et al. 2023), rhodamine B dye (RhB) (Muraro et al. 2020), fast green FCF and methyl orange (Park et al. 2017), and malachite green and congo red dyes (Zheng et al. 2020) is achieved by using various metal oxide SnO 2 , Ti/Ag/ Fe 2 O 3 -based catalysts are reported. To date, WO 3 nanostructures with twin-tail-based gemini surfactants are not reported (Systronics 2202).
In this work, the WO 3 nanostructures in the presence of gemini surfactants by using the simple hydrothermal method and also compared their photocatalytic activity with the conventional surfactant, i.e., C 14 TAB derived tungsten oxide nanostructures. The effects of using the gemini surfactants and C 14 TAB on size and morphology as well as the impact of change of size and morphology in photocatalytic degradation of the fast green (FCF) dye were discussed in detail. For the first time, the effect of gemini-based twin-tail and conventional surfactant on tungsten oxide nanostructures and their efficacy for the elimination of the organic pollutant is studied.

Synthesis of WO 3 nanostructures
The synthesis of WO 3 nanoparticles was carried out by taking the 1 mM of NaWO 3 .H 2 O solution prepared in 20 mL of deionized water with constant stirring, 1 mM of TTS in 15 mL of deionized water followed by 4 mL of 2 M HCl aqueous solution in a dropwise manner with constant stirring. The solution was left for constant stirring for the next 30 min. At this point, the texture of the solution was milkish white. Finally, the resultant solution was transferred to the sealed teflon-lined stainless steel autoclave. The sealed autoclave was heated to 110 °C for 5 h. After completion of the reaction, the yellow-colored precipitates were collected by centrifuging and washed several times with deionized water, followed by vacuum oven drying. On the other hand, for the second sample, the TTS was replaced with the conventional C 14 TAB, and the rest of the procedure was similar for the preparation of tungsten oxide nanostructures.

Characterization
The formation of WO 3 nanoparticles through the hydrothermal method is confirmed by X-ray diffraction (XRD) analysis. The X-ray diffraction patterns were recorded using Panalytical's X'Pert Pro diffractometer with graphite monochromatized CuK α irradiation (λ = 1.5418 Å). The infrared spectrum was measured by Perkin Elmer-Spectrum RX-IFTIR, Fourier transform infrared spectrometer (FTIR) at room temperature in the range of 4000-400 cm −1 . High-resolution transmission electron microscopy (HR-TEM) images, EDS, and elemental mapping were recorded on FEI Tecnai G2 20S-TWIN. UV-visible spectra were analyzed by using a UV-visible spectrophotometer (Systronics 2202) in the range of 200-900 nm.

Photocatalytic analysis
The photocatalytic aptitudes of synthesized WO 3 nanostructures were assessed via the degradation of FCF pollutant under sunlight irradiation. All photocatalytic investigations were carried out under parallel conditions on sunny days between 10 am and 2 pm. Open borosilicate glassware was used for the reaction (Balakrishnan et al. 2017). In the degradation studies, 20 mg of the synthesized photocatalyst was suspended in 50 mL of an aqueous solution comprising FCF dye at a concentration of 1 × 10 −5 M. At the start of the experiment, before visible light irradiation, to attain adsorption-desorption equilibrium between the pollutants and tungsten oxide nanoparticles, the solution was magnetically stirred in the dark for 30 min. At the given time interval, 3 mL of the suspension was sampled and centrifuged at 4000 rpm for 15 min to separate the tungsten oxide nanoparticles from the solution. The supernatant liquid was examined for the residual concentration of the FCF dye under study. The FCF dye was studied by recording the deviations in absorbance at the representative absorption peak of λ = 620 nm in addition to scanning over the wavelength from 300 to 800 nm using a UV-Vis spectrophotometer.
To evaluate the photocatalytic activity of tungsten oxide nanoparticles for pollutant degradation, assorted reaction parameters such as reaction time, amount of photocatalyst, the concentration of the organic pollutant, and the effect of different pH were analyzed in detail. The aliquots of the mixture were taken at a definite interval of time during the irradiation, and after centrifugation of the photocatalyst, absorbance was measured. The degradation percentage of the FCF after photoreaction for the time (t) was analyzed as (Ramanathan et al. 2020). (1)

Morphology analysis
The morphology of WO 3 nanostructures synthesized using C 14 TAB and TTS was studied by employing high-resolution transmission electron microscopy, shown in Fig. 1. It can be observed that WO 3 nanostructures of different shapes and sizes were obtained by the use of C 14 TAB and TTS surfactants. The WO 3 web of chains obtained with the C 14 TAB is shown in Fig. 1a. The HR-TEM image in Fig. 1b reveals that the surfactant directs the continuous growth of the WO 3 web of chains possessed of fused nanostructure. On the other hand, cube-shaped WO 3 nanoparticles were obtained using TTS surfactant, as shown in the low and high magnification TEM images Fig. 1c and d. The inset in Fig. 1d demonstrates the high-resolution image confirming the d-spacing value 0.35 nm corresponds to the (111) plane of the WO 3 cube-shaped nanoparticles. The average particle size observed from the HR-TEM analysis for the WO 3 web of chains was ~ 35 nm and for WO 3 cube-shaped nanoparticles was ~ 15 nm, respectively. The nanoparticles size reduction by 50% confirms that the lower cmc value of TTS surfactant compared to conventional surfactants is significant to tune the size of metal oxide-based nanomaterials and acts as shape directing and stabilizing agent for the development of nanostructures.
As it is clear from the molecular structure, CTAB is a single tail/monomeric surfactant and TTS is a double tail/ dimeric surfactant, are schematically shown in scheme S1. There is a considerable difference in the shape and size of the WO 3 nanostructures. The double tail surfactants demonstrate very high potential for the shape as well as size control effects because of their greater interfacial adsorption ability, and great hydrophobicity are known as more surface-active in comparison to their monomeric units or conventional surfactants and therefore, they have been successfully used as shape directing agent for the synthesis of desired morphologies (Jamwal et al. 2016a). The TTS surfactant leads to the formation of cube-shaped nanoparticles due to the presence of twin-tails which results in major growth along the (111) and (020) planes (see XRD spectra in Fig. 2). On the other hand, in the case of WO 3 web of chains, planes responsible for the particles growth were the same, i.e., (111) and (020) but there is a change in the morphology as well as size, the formation of the diffused chain-like structures in WO 3 web of chains may C 0 = initial dye concentration, C 1 = residual dye concentration at t minutes be due to the coalescence in the particles supported by the conventional surfactant consist of single chain. The coalescence behavior in the nanoparticles arises with contact and initial fusion trailed by the orientational alignment of the coalescing planes at the interface among the particles during contact. Furthermore, the crystal structure analysis of the samples was also performed by selected area diffraction pattern (SAED). The SAED patterns of WO 3 web of chain and WO 3 cube-shaped nanoparticles are shown in Fig. 1e and f which indicate the polycrystalline nature of both nanostructures. The indexed SAED rings confirm the orthorhombic structure of the WO 3 nanostructures. Similar lattice spacing values were obtained for both WO 3 nanostructures synthesized using C 14 TAB and TTS surfactants. However, the ordered SAED pattern of TTS-derived WO 3 cube-shaped nanoparticles indicates the better crystalline character of cube-shaped nanoparticles. Clearly, the TTS surfactant has an edge over conventional surfactant for synthesizing the nanoparticles, which can be due to the lower cmc and existence of twin-tails in the TTS surfactant executes stable growth of nanoparticles in comparison to the single tail C 14 TAB. In our recent investigation, the chain length and spacer between the twin-tail has been also found effective to control the shape and size of gold nanoparticle (Rana et al. 2016). The composition of the samples was analyzed through EDX and elemental mapping. Figure 1g and h show the EDX of the WO 3 nanostructures representing the presence of W and O elements, which validate the formation of the WO 3 nanoparticles with no extra impurity peaks. The presence of carbon in both samples is attributable to the organic stabilizing agent as well as to the carbon-coated microgrid mesh supporting the samples for the analysis. The presence of copper peaks also belongs to the microgrid. The atomic percentages of W and O in the case of the web of chains nanostructure were found as 4.99% and 15.56%, respectively. In the same way, for the WO 3 cube-shaped nanoparticles, the atomic percentages of W and O were found as 5.55% and 17.67% respectively and the ratio for the respective elements was also found around 1:4. Figure 1i and j show the elemental mapping for the distribution of the elements, i.e., W, O, and C in the prepared WO 3 web of chains and WO 3 cubeshaped nanoparticles, respectively.

XRD analysis
The structural identification of the as-prepared nanostructures was confirmed by using the X-ray diffraction (XRD) analysis. The XRD patterns of WO 3 nanostructures prepared with C 14 TAB and TTS surfactants are summarized in Fig. 2 , and (133) planes of the orthorhombic phase for the tungsten oxide hydrate (ICDD:01-084-0886). Notably, a nearly identical XRD pattern was observed for both cases. The Debye-Scherrer equation was applied to calculate the average crystallite size of the prepared WO 3 nanostructures. The crystallite size calculated from XRD was found as 50 and 40 nm for the C 14 TAB and TTS-derived nanoparticles, respectively. The crystallite size acquired from the Debye-Scherrer formula of size calculation lacks the contribution from the lattice strain parameters which also indicates the broadening in the XRD peaks (Bakr et al. 2021). For thorough structural properties investigation of the nanostructures, it is important to acquire information on the other parameters such as the size, strain, stress, and energy density. Thus, Williamson-Hall (W-H) plot method is used to excerpt an appropriate understanding of the aforesaid parameters by using the XRD analysis (Sheikh et al. 2018;Kibasomba et al. 2018). The aforementioned parameters were obtained from the various models, i.e., uniform deformation model (UDM), uniform stress deformation model (USDM), and uniform deformation energy density model (UDEDM) under W-H analysis are summarized in Table 1. The plots for the W-H analysis models are shown in the Fig. S1. Through these models, the parameters, for instance, lattice strain, stress, and energy density of the system, were determined within a certain approximation. Furthermore, it should be noted that the W-H method provides information about the divergence between the size and strain broadening analysis. Because the basic Scherrer-equation depends on 1/cos Ѳ, where the W-H method follows tan Ѳ. The major difference shows the existence of microstrain and variation in the crystallite size as given in Table 1. Among them, existence of lattice strain among nanograins may effect on photocatalytic behavior. Generally, the lattice strain enhance the transitions of photocarriers along with the trapping possibilities of holes. As per uniform deformation model calculations, cube-shaped nanoparticles show 44 times higher compressive strain compare to the web of chains, which may contribute to the photocatalytic degradation.

UV-Vis analysis
The optical properties of the samples were analyzed by using UV-VIS absorption spectra. Figure 3a shows the absorption spectra of the synthesized WO 3 web of chains and WO 3 cube-shaped nanoparticles. Here, the characteristic spectrum with its fundamental absorption sharp edge rises at around 407 nm and 400 nm, correspondingly. The red shift in the absorption edge in the case of the WO 3 web of chains was observed, where, it was slightly shifted toward a higher wavelength with a difference of ~ 7 nm. The optical band where α is the absorption coefficient, A is a constant, hv is the photon energy, E g is the optical band gap, and n is the possible electronic transition. The band gap energies of the WO 3 web of chains and WO 3 cube-shaped nanoparticles were valued to be 2.66 and 2.69 eV, respectively (Fig. 3b).
As is clear, the band gap energy is higher for the smallersized nanoparticles and directly supported by the quantum confinement theory, which proposes that the electrons in the conduction band and holes in the valence band are confined by the potential barriers of the surface or potential well of the quantum box. Thus, due to the confinement of the electrons and holes, the band gap energy increases between the valence band and conduction band with decreasing particle size (Edvinsson 2018;Singh et al. 2019).

FTIR analysis
The perceived bands for the pure C 14 TAB and TTS as well as both with WO 3 web of chains and WO 3 cube-shaped (2) ahv = A(hv − E g ) n Table 1 Geometric parameters of WO 3 web of chain and cube-shaped nanoparticles nanoparticles were studied to enumerate the surface adsorption of the surfactants on the surface of nanostructures, which is summarized in Fig. 4. Focusing on the pure C 14 TAB and WO 3 web of chains (Fig. 4a), the characteristics bands at 2914 cm −1 (CH 2asym ) shifts to 2919 cm −1 , 2846 cm −1 (CH 2sym ) shifts to 2849 cm −1 , 1480 cm −1 (δ(CH 3 ) asym ) shifts to 1489 cm −1 , 1408 cm −1 (CH 2 )n sciss shift to 1376 cm −1 , 909 cm −1 v(C-N + ) shifts to 864 cm −1 and 715 cm −1 (CH 2 ) rock shifts to 648 cm −1 in case of pure C 14 TAB to WO 3 web of chains. The other bands at 3016 cm −1 (CH 3asym (-N + (CH 3 ) 3 ), 2946 cm −1 (CH 3sym (-N + (CH 3 ) 3 ), 1462 cm −1 (CH 2 )n sciss , and 949 cm −1 v(C-N + ) for pure C 14 TAB were not observed in WO 3 web of chains, indicating the strong interaction of the surfactant with the web of chains (Borodko et al. 2009). Furthermore, in the case of TTS (Fig. 4b), the bands at 2954 cm −1 , 2922, and 2851 correspond to symmetric (v sym (C-H)) and asymmetric (v asym (C-H)) stretching vibrations of methylene groups, respectively, which shifts to 2950, 2915, and 2850 in the case of WO 3 cube-shaped nanoparticles. The band related to NR 4 + asymmetric bending (ρ asym (NR 4 + )) at 1636 was shifted to 1625 for WO 3 cube-shaped nanoparticles. Furthermore, the scissoring mode of vibration for the methylene chains (C-H) was observed at 1463 and 1378 moved to 1465, an indicator of the gauche defects. The band at 971 can be assigned to the v(C-N + ) stretching modes that shifted to 953. The band at 853 for pure surfactants was observed and showed a shift to 887 which may be a pointer to higher energy end-gauche defects than in pure TTS and proposes that the head group of the surfactant is intensely attached to the nanoparticles. The absence of the bands in the case of WO 3 cube-shaped nanoparticles was an indication of the strong interaction of the surfactants with the nanoparticles (Jamwal et al. 2016b). The peak assignment for the pure surfactants and nanoparticles synthesized in the presence of surfactants is mentioned in Table 2.
Based on the above results, we identified a possible formation reaction mechanism of WO 3 nanostructures synthesized with C 14 TAB and TTS surfactants. In the hydrothermal method, the synthesis of WO 3 starts with the formation of tungstic acid. The reaction between Na 2 WO 4 .2H 2 O and HCl in the presence of C 14 TAB and TTS has been shown in Eqs.
(3) and (4). The formation of tungsten oxide nanostructures in this hydrothermal process has been considered a direct combination pathway:

Degradation of FCF dye with WO 3 nanostructures under sunlight
The photocatalytic activity of the synthesized nanostructures was appraised for the fast green dye degradation as an exemplary reaction under visible light irradiation. By monitoring the maximum absorbance of the FG at 620 nm, the photocatalytic degradation of the FCF dye was represented in Fig. 5, showing the plot between normalized concentration and the analogous time. The reaction for the decomposition of the FG dye obeys the first-order reaction, which could be shown by the following equation (Alzahrani 2018): where C 0 represents the concentration of the FG at a time equal to zero (equilibrium), C is the concentration at any time, and k represents the rate constant of the reaction. The first-order equation speculates that the bindings originated from physical adsorption. It can be observed clearly from Fig. 5a and c that in the presence of solar irradiation, the WO 3 web of chains as a catalyst took 190 min for the 86% degradation of the FG dye with the rate constant value as k = 0.0117 min −1 . Similarly, in the case of WO 3 cube-shaped nanoparticles, the maximum absorbance of FG at 620 nm was shown and 94% degradation with k as 0.0134 min −1 was observed from the plot ( Fig. 5b and d). Based on the aforementioned data, it has been observed that WO 3 cubeshaped nanoparticles were showing a worthy performance in comparison to the WO 3 web of chains. The higher photocatalytic degradation efficiency can be attributed to the smaller size nanoparticles synthesized in the presence of TTS. The photoreactions mainly proceed on the surface of the photocatalyst and a decrease in the size of nanoparticles will lead to the increase in surface area to volume ratio, available surface-active sites, and interfacial charge carrier transfer rates which directly point towards the higher catalytic activities. By following Eq. (5), the first-order reaction rate constants were calculated for the WO 3 web of chains and WO 3 cubeshaped nanoparticles and are shown in Fig. 6a and d. The plot shows a straight line fit with a correlation coefficient very close to unity (r 2 = 0.988 for the WO 3 web of chains and 0.998 for WO 3 cube-shaped nanoparticles), clearly indicating that the kinetics of the degradation reaction followed the first-order rate law. Adsorption of FCF onto the catalyst was also evaluated for the pseudo-second-order ( Fig. 6b and e) and intraparticle diffusion model where, Q e and Q t are the adsorption capacity of tungsten oxide nanoparticles at equilibrium and at time t (min). The initial adsorption rate was found using k 2 Q e 2 . On the other hand, the intraparticle diffusion model was applied to identify the diffusion mechanism. The equation of the intraparticle diffusion model is shown as: where k i represents the intraparticle diffusion rate and C is the intercept. The linearized results from the aforementioned kinetic models are compiled in Table 3.
The correlation coefficient (R 2 ) and the kinetic results obtained from different models signify that the adsorption of FCF is controlled by the pseudo-first-order model in comparison to the other, i.e., pseudo-second-order and intraparticle diffusion model.
It has been noted that, in semiconductor materials, the band edge positions have a considerable connection with the oxidation process of organic compounds. Therefore, it is compulsory to determine the valence band (VB) and where, χ is the absolute electronegativity of the semiconductor atom and the value of χ for the WO 3 was determined as 6.88 eV (Aslam et al. 2019), E C is the energy of free electrons of the hydrogen scale, i.e., kinetic energy of the electrons and Eg for the WO 3 web of chains, and WO 3 cube-shaped nanoparticles were calculated as 2.66 and 2.69 eV, respectively, by using the Eq. 1. Based on Eqs. 8 and 9, the values for the VB and CB for WO 3 web of chains were extracted as 1.05 and 3.71 eV. Similarly, for the WO 3 cube-shaped nanoparticles, VB and CB values were found as 1.03 and 3.72 eV, respectively. A pictorial representation of the photocatalytic . 6 a and d Pseudo firstorder kinetic model, b and e pseudo second-order kinetic model, and c and f for photodegradation of FCF dye in the presence of WO 3 web of chains and WO 3 cube-shaped nanoparticles which are present at the lower potential (1.05 and 1.03 eV) for both systems got excited by absorbing the photons with energy hv ˃E g and move to the conduction band having the higher potential (3.71 and 3.72 eV). The charge carriers generated due to this process participate in the oxidation and reduction process during the photocatalytic reaction. In detail, due to the presence of visible light irradiation, the photocatalyst was activated to generate the pairs of holes (h + ) and electrons (e − ).
The photogenerated holes reacted with H 2 O to form hydroxyl radical ·OH, which is the major oxidant species to degrade the different organic pollutants and hydrogen ions (H + ), which acts as a byproduct and resulted in the decrease of pH in the system. The generation of the electrons in the reaction was responsible to create other oxidants by consuming the oxygen that can be oxidized directly by the active radicals to final products as CO 2 and H 2 O. Due to the above-mentioned reaction steps, the different nanomaterial photocatalysts perform with admirable photocatalytic efficiency. The degradation of the organic dye by the active species can be proposed as (Yu et al. 2020):

Conclusion
In summary, we have successfully synthesized the WO 3 nanostrucutres by a simple one-pot synthesis incorporating the two completely different shape and size directing agents, i.e., TTS and C 14 TAB, resulting in enormous changes in the shape and size of the prepared nanoparticles. The detailed structural analysis was supported by XRD, EDS, and elemental mapping. The optical measurements indicated that the prepared nanoparticles are favorable for the photocatalytic decomposition of the organic pollutant. The effect of size on the degradation of the organic pollutant was also observed and discussed in detail. It was observed that the nanoparticles prepared with TTS were smaller in size and show greater photocatalytic efficiency of 94% for the FCF dye. As a consequence, the obtained nanoparticles, by controlling the shape and size by varying the parameters, could be a potential candidate for solar light-based wastewater treatment.
Author contribution Deepika Jamwal and Jae Young Park: investigation, data curation, analysis, original draft writing, visualization, and conceptualization. Vishal Mutreja and Rahul: formal analysis and visualization. Surinder Kumar Mehta: conceptualization, review, and editing. Akash Katoch: review and editing, conceptualization, and visualization. Sang Sub Kim: visualization, review, and editing.
Funding Deepika Jamwal acknowledges financial support from a National Post-Doctoral Fellowship (PDF/2017/001869), from the DST, SERB, India, Chandigarh. Akash Katoch acknowledges financial support from UGC-Startup Grant. The authors also acknowledge the research and laboratory facility support from Panjab University, Chandigarh.
Data availability All data generated or analyzed during this study are included in this article.

Declarations
Ethical approval and consent to participate Not applicable.

Consent for publication
All authors read and approved the final manuscript. All authors are fully aware of this manuscript and have permission to submit the manuscript for possible publication.

Conflict of interest
The authors declare no competing interests.

References
Ahmed MA, Brick AA, Mohamed AA (2017)  Scheme 1 Schematic representation of the photocatalytic mechanism for the degradation of fast green (FCF) in the presence of WO 3 web of chains and WO 3 cube-shaped nanoparticles