WO3 Composites Research Articles

Synthesis of Photocatalyst Based on WO3 Applying for the Treatment of Tetracycline Antibiotics

In this paper, WO3/g-C3N4 photocatalysts were fabricated by ultrasonic-assisted hydrothermal method at different mole ratios of WO3/g-C3N4. Ultraviolet–visible absorption spectroscopy (UV-Vis DRS) and photoluminescence (PL) results indicated that WO3/g-C3N4 photocatalyst with the WO3/g-C3N4 mole ratio of 1/1 (WC-1) showed visible light absorption ability and prevented electron-hole recombination rate better than WO3, g-C3N4 and other composites. The photocatalytic activities of synthesized photocatalysts were investigated by the photocatalytic oxidation of tetracycline (TC) antibiotics under visible light. The degradation efficiency of TC in aqueous environment by the WC-1 was 79.35% after 180 minutes. This value was higher than those of other materials. The improvement in photocatalytic property of the WO3/g-C3N4 was due to the efficient generation of electrons and holes.

Composites Based on Electrodeposited WO3 and TiO2 Nanoparticles for Photoelectrochemical Water Splitting.

Photoelectrochemically active WO3 films were fabricated by electrodeposition from an acidic (pH 2), hydrogen-peroxide-containing electrolyte at -0.5 V vs. SCE. WO3-TiO2 composites were then synthesized under the same conditions, but with 0.2 g/L of anatase TiO2 nanoparticles (⌀ 36 nm), mechanically suspended in the solution by stirring. After synthesis, the films were annealed at 400 °C. Structural characterization by XRD showed that the WO3 films exhibit the crystalline structure of a non-stoichiometric hydrate, whereas, in WO3-TiO2, the WO3 phase was monoclinic. The oxidation of tungsten, as revealed by XPS, was W6+ for both materials. Ti was found to exist mainly as Ti4+ in the composite, with a weak Ti3+ signal. The efficiency of the WO3 films and composites as an oxygen evolution reaction (OER) photo-electrocatalyst was examined. The composite would generate approximately three times larger steady-state photocurrents at 1.2 V vs. SCE in a neutral 0.5 M Na2SO4 electrolyte compared to WO3 alone. The surface recombination of photogenerated electron-hole pairs was characterized by intensity-modulated photocurrent spectroscopy (IMPS). Photogenerated charge transfer efficiencies were calculated from the spectra, and at 1.2 V vs. SCE, were 86.6% for WO3 and 62% for WO3-TiO2. Therefore, the composite films suffered from relatively more surface recombination but generated larger photocurrents, which resulted in overall improved photoactivity.

Facile construction of efficient WO3/V2O5 coupled g-C3N4 ternary composite photocatalyst for environmental emergent aqueous pollutant degradation: Stability, degradation reaction pathway and effect of pH evaluation.

Currently, one of the primary challenges that human society must overcome is the task of decreasing the amount of energy used and the adverse effects that it has on the environment. The daily increase in liquid waste (comprising organic pollutants) is a direct result of the creation and expansion of new companies, causing significant environmental disruption. Water contamination is attributed to several industries such as textile, chemical, poultry, dairy, and pharmaceutical. In this study, we present the successful degradation of methylene blue dye using g-C3N4 (GCN) mixed with WO3 and V2O5 composites (GCN/WO3/V2O5 ternary composite) as a photocatalyst, prepared by a simple mechanochemistry method. The GCN/WO3/V2O5 ternary composite revealed a notable enhancement in photocatalytic performance, achieving around 97% degradation of aqueous methylene blue (MB). This performance surpasses that of the individual photocatalysts, namely pure GCN, GCN/WO3, and GCN/V2O5 composites. Furthermore, the GCN/WO3/V2O5 ternary composite exhibited exceptional stability even after undergoing five consecutive cycles. The exceptional photocatalytic activity of the GCN/WO3/V2O5 ternary composite can be ascribed to the synergistic effect of metal-free GCN and metal oxides, resulting in the alteration of the band gap and suppression of charge recombination in the ternary photocatalyst. This study offers a better platform for understanding the characteristics of materials and their photocatalytic performance under visible light conditions.

High-performance electrochromic WO3/POM–MXene energy storage device with color-based energy indication

Electrochromic energy storage devices (EESDs) with quantitative color-based visualization of their energy state have applications in smart displays and wearable intelligent electronics, as well as energy-efficient buildings. In addition, because of their ability to display their energy storage state accurately and in real time, the overcharging of energy-storage devices can be prevented, thus improving safety. WO3 is a classical electrochromic material, but EESDs based on WO3 can suffer from low coloration efficiencies and energy densities, as well as short cycle lives. However, compositing is a promising way to improve these properties. Therefore, in this study, an electrochromic WO3 nanoblock (NB)/Preyssler-type K12.5Na1.5[NaP5W30O110]-15H2O polyoxometallate (P5W30)//Ti3C2TX MXene energy storage device was prepared by a simple hydrothermal method. The WO3NB/P5W30 film was first deposited on a conductive substrate as the cathode and subsequently modified with the MXene film as the anode. The device exhibited a high coloration efficiency (145.02 cm2/C), excellent energy density (9.8 × 10−3 mWh/cm2), long cycle life (62.5 % retention rate after 5000 galvanostatic charge–discharge cycles), and excellent chromaticity difference (ΔE*, 25.91). These properties are not only due to the unique 2D layered structure of MXene but also the greater compatibility between the cathode and the anode (as shown by the q-values). In addition, compared to a WO3NB film alone, the composite WO3NB/P5W30 film had higher areal capacitance (12-times higher) and ΔE* (11-times higher), which is attributed to the synergism between the crystalline WO3 and amorphous polyoxometallate composite. This study provides an effective method for developing high-performance EESDs with quantitative color-based charge-state visualization and long cycle lives.

Rationally designed MIL-101(Fe)/WO3 S-scheme heterojunction coupled with peroxymonosulfate for boosting the visible-light-driven photodegradation of tetracycline hydrochloride

Developing S-scheme photocatalysts with excellent catalytic activity and convenient retrieval is highly desirable for wastewater purification. Herein, a novel S-scheme MIL-101(Fe)/WO3 heterojunction on carbon cloth is successfully synthesized via a facile solvothermal approach. The optimized MIL-101(Fe)/WO3 composite (MWC-1.5) has been found to be highly effective in activating peroxymonosulfate (PMS) and then degrading tetracycline hydrochloride (TC-HCl) with a 100% degradation rate when exposed to visible light (Vis) within a period of 20 min. Such MWC-1.5/PMS/Light system also shows stable cycling performance and good recyclability. The remarkable photocatalytic degradation performance is mainly attributed to the powerful intrinsic electric field that accelerates the separation of photogenerated charge carriers via the S-scheme charge transfer. Radical quenching experiments and electron paramagnetic resonance (EPR) results suggest that SO4– and OH are the major oxidizing substances in the photocatalytic processes. Three potential degradation pathways are deduced based on an in-depth analysis of the degradation intermediates and the degradation mechanism is also elucidated through a rational combination of the experimental studies and theoretical calculations. This novel hybrid photocatalyst system has been shown to be a promising strategy for environmental remediation, while also suggesting a feasible approach for the development of photocatalysts with both remarkable activity and stability.

A Z-scheme heterojunction ZIF67/N, P-WO3 nanocomposite for photocatalytic degradation of levofloxacin

In this work, a ZIF67/N, P-WO3 (ZNPW) Z-scheme heterojunction was constructed by N, P-codoped WO3 (NPW), and ZIF67 and developed as a highly efficient photocatalyst for Levofloxacin (LFX) removal. A series of characterization measurements including FTIR, XRD, SEM, DRS, PL, and XPS are conducted to confirm the formation of the ZNPW. After optimization on the composition of WO3, NPW and ZIF67, the optimal ZNPW shows superior photocatalytic activity, yielding a higher removal efficiency of LFX ∼91.2% in 100 min than those of pure WO3 (9.4%), NPW (47.8%) and ZIF67 (14.3 %). Additionally, ZNPW exhibits remarkable stability and reusability for up to five consecutive runs. Reactive species scavenging experiments and ESR have revealed that the degradation of LFX is primarily facilitated by the generation of holes (h+) and hydroxyl radicals (·OH). Moreover, the degradation process of LFX was identified through an integrated LC-MS analysis and density functional theory computation of the Fukui indices. This process consists of three pathways: the opening of the piperazinyl ring, separation of piperazinyl and quinoline moieties, and cleavage of the pyridine ring on the quinoline moieties. The superior photocatalytic properties can be attributed to the N, P co-doping in the WO3 structure and the simultaneous coupling with ZIF67, leading to the formation of a heterojunction with a reduced band gap, efficient charge separation and transport, and a new N 2p and P 2p energy level. In conclusion, this study provides novel insights into designing high-efficiency antibiotics degradation using WO3-based Z-scheme heterojunction photocatalysts.

Interconnected SnO2 nanoflakes decorated WO3 composites as wearable and ultrafast sensors for real-time wireless sleep quality tracking and breath disorder detection

Monitoring human breath is critical for determining human well-being. Most reported humidity sensors are unsuitable for breath monitoring because of their long response and recovery time, poor stability, and high operating temperature. To address these challenges, robust tungsten oxide (WO3) and tin oxide (SnO2) composite sensors were fabricated, and their humidity-sensing properties were investigated. The SnO2/WO3 composites were optimized by altering the SnO2 fraction to achieve high humidity sensitivity. The SnO2/WO3 composite exhibited superior sensing performance (88) than pristine WO3 and SnO2 under 97 % relative humidity. The sensor demonstrated good linearity while altering humidity from 15 % to 97 %, with an R2 = 0.9729. The sensor's rapid response (0.6 s) and recovery (0.6 s) time allow for breath rate monitoring and breath disorder detection. The wearable sensor demonstrated multifunctional human breath detections such as varied breath rates (5–60 breaths per minute), nose blocking for separate nostrils, wireless sleep quality tracking for more than 7 h continuously, and sleep apnea-hypopnea detection via a smartphone. The capabilities of the humidity sensor allow for robust application in sleep quality, sleep apnea, and hypopnea detection.

In-situ construction of g-C3N4/WO3 heterojunction composite with significantly enhanced photocatalytic degradation performance

g-C3N4/WO3 heterojunction composites were synthesized via an in-situ method by thermal polymerizing the mixture of dual precursors (urea and thiourea with molar ratio of 3:1) and different amount of tungstic acid. The as-synthesized g-C3N4/WO3 composites, with lamellar and rod-like nano-porous structure, were mainly composed of g-C3N4 and monoclinic WO3, in which the crystal size of WO3 was about 5–10 nm. The specific surface area of the composite increased gradually with the tungstic acid dosage and reached 79.41 m2/g when the addition amount of tungstic acid was 1 wt%. The in-situ construction of g-C3N4/WO3 heterojunction contributed to the reduction of band gap, improvement of the visible response range as well as the acceleration of the separation and migration of the photogenerated carriers. As the dosage of tungstic acid increased, the photocatalytic degradation performance of g-C3N4/WO3 composite towards tetracycline improved gradually and achieved the optimum when the addition amount of tungstic acid was 0.1 wt% (CN/WO3-10). CN/WO3-10 (0.05g) degraded 83 % of tetracycline molecules (100 mL, 20 mg/L) after photocatalysis for 100 min, whose degradation rate constant was 10.1 and 1.48 times that of pure WO3 and g-C3N4, respectively. Moreover, g-C3N4/WO3 composite exhibited excellent stability and reusability for the photocatalytic degrading tetracycline. This work provides a facile and practicable approach for the preparation of g-C3N4/WO3 composite.

A disposable sensor based on one-pot synthesized tungsten oxide nanostructure-modified screen printed electrodes for selective detection of dopamine and uric acid.

Here, screen-printed carbon electrodes (SPCEs) were modified with ultrafine and mainly mono-disperse sea urchin-like tungsten oxide (SUWO3) nanostructures synthesized by a simple one-pot hydrothermal method for non-enzymatic detection of dopamine (DA) and uric acid (UA) in synthetic urine. Sea urchin-like nanostructures were clearly observed in scanning electron microscope images and WO3 composition was confirmed with XRD, Raman,FTIR and UV-Vis spectrophotometer. Modification of SPCEs with SUWO3 nanostructures via the drop-casting method clearly reduced the Rct value of the electrodes, lowered the ∆Ep and enhanced the DA oxidation current due to high electrocatalytic activity. As a result, SUWO3/SPCEs enabled highly sensitive non-enzymatic detection of DA (LOD: 51.4nM and sensitivity: 127µAmM-1cm-2) and UA (LOD: 253nM and sensitivity: 55.9µAmM-1cm-2) at low concentration. Lastly, SUWO3/SPCEs were tested with synthetic urine, in which acceptable recoveries for both molecules (94.02-105.8%) were obtained. Given the high selectivity, the sensor has the potential to be used for highly sensitive simultaneous detection of DA and UA in real biological samples.

Fabrication of Ru/WO3-W2N/N-doped carbon sheets for hydrogen evolution reaction

Recent experimental analysis indicates WO3-based nanostructures exhibit poor hydrogen evolution reactivity, particularly in alkaline medium, arising from the low electron transfer rate. It is imperative to tune the composition and structure of WO3 to boost the cleavage of H-OH bond. Here, we construct Ru/WO3-W2N/N-doped carbon sheets (Ru/WO3-W2N/NC) using m-WO3 nanosheets as precursors with the aid of RuCl3, Tris (hydroxymethyl) aminomethane, and dopamine. Structural investigation reveals the formation of N-doped carbon sheets, Ru nanoparticles, and WO3-W2N. As a result, hydrogen evolution reactivity is greatly improved on Ru/WO3-W2N/N-doped carbon sheets with 64 mV at 10 mA/cm2 in 1 mol/L (M) KOH, outperforming most of WO3-based electrocatalysts in previous literatures. Meanwhile, it facilitates the generation of H2 in 0.5 M H2SO4 with the excellent activity of 110 mV at 10 mA/cm2. Our work provides an efficient strategy to tailor the electronic structure of WO3 to catalyze acidic and alkaline hydrogen evolution reaction.

Nanoparticulate films of WO3 and MoO3 composites for enhancing UV light electrochromic transmittance variation and energy storage applications

Green technologies for the manufacture of optical shutters retain a sustainable development. In this work, the electro-exploding wires and spray coating technologies are employed to deposit nanoparticulate (WO3)1-x(MoO3)x composite films. MoO3 NPs are introduced to enhance electrochromic (EC) transmittance variation of violet and UV light with wavelengths ranging from 330 to 450 nm. Measurements of EC performances of (WO3)1-x(MoO3)x composite films in a potentiostat are carried out to discern beneficial from MoO3 addition. It is observed that the diffusion coefficient and the charge density increase with an increment of MoO3 concentration. The coloration efficiency at 430 nm raises apparently whereas that at 633 nm does not show a significant variation with increasing MoO3 concentrations. In addition, the EC device with ∼12.5% of MoO3 introduced reveals a much higher optical modulation at 430 nm. From the measurements of galvanostatic charge-discharge curves of EC films in the potentiostat, the areal capacitances of 12.9 and 14.0 mF/cm2 are estimated for pure and ∼12.5% MoO3 introduced WO3 EC films. The EC batteries are demonstrated and the enlarged energy storage capability with an addition of MoO3 is observed. The simple introduction of MoO3 into WO3 nanoparticulate films compensates drawbacks of WO3 films and enhances EC performances and energy storage capabilities.

Preparation and properties of water‐based photochromic polyurethane coatings containing Er(III)‐doped WO3

Photochromic coatings have been widely used in many fields such as architecture, transportation, and military because of the combination of reversible color‐changing properties with the insulation and protection of substrates. Conventionally, organic photochromic components are used for the preparation of photochromic coatings with fast photo‐response and excellent fatigue resistance, but the preparation of these coatings is costly and time‐consuming. Here, we have developed a relatively simple and cost‐effective strategy for the preparation of water‐based photochromic polyurethane coatings. Er(III)‐doped WO3 was synthesized and used as the photochromic component for the preparation of polyurethane/Er(III)‐doped WO3 composites, which were further used for the preparation of photochromic coatings. The properties of the coatings were tested and characterized. Due to their excellent thermal stability, water resistance, fatigue resistance, and photochromism, these coatings might have practical applications in various areas.

Passive and wireless NFC tag-type trimethylamine gas detection based on WO3/MXene composite sensors

In this paper, we developed a high-sensitive WO3/MXene composite based gas sensor. The morphology, crystal structure, and chemical composition of the pure WO3, MXene and WO3/MXene composite were analyzed by several characterization means include SEM, XRD, and XPS, proving that the successful synthesis of WO3 nanoparticles, MXene nanosheets and WO3/MXene composites. The trimethylamine sensing element was fabricated by spin coating the prepared sensitive materials on the interdigital electrodes. The gas-sensing performance of the sensor was investigated at 25 oC, 23% RH, and the results demonstrate that the WO3/MXene based sensor has excellent response (Ra/Rg = 277.78 @10 ppm), fast response/recovery time (2 s/3 s @ 2 ppm) towards trimethylamine. It also holds excellent repeatability, selectivity, short-term and long-term stability. As a result, we have found that the addition of MXene has greatly improved the performance of WO3 for trimethylamine detection at room temperature. Finally, a tag-type gas detection device based on NFC technology has been developed to achieve detection. When testing, we only need to place a sensor label without power supply in the gas environment, and the non-contact testing can be realized outside. This work presents a novel, safe method for realizing hazardous gas detection.

Boosting Photocatalytic N2 Fixation on N‐Defect g‐C3N4/WO3: the Synergistic Effects of Nitrogen Vacancy and Z‐Scheme Heterojunction

AbstractPhotocatalytic nitrogen fixation is a promising strategy for ammonia synthesis under mild conditions by using solar energy, but N2 activation remains a great challenge. Herein, we demonstrate that a Z‐scheme g‐C3N4/WO3 heterojunction possessing abundant nitrogen vacancies exhibits the highly enhanced activity for photocatalytic N2 fixation through efficient nitrogen molecular activation compared with pristine NVs‐g‐C3N4 and WO3 photocatalysts. The construction of the internal electric field induced by Z‐scheme NVs‐g‐C3N4/WO3 heterojunction allows a rapid charge carrier separation and simultaneously maintains the powerful redox ability of photogenerated charge carriers, defined by the covalent CO bond. Moreover, nitrogen vacancy plays a crucial role in the adsorption/activation of N2, which substantially facilitates the hydrogenation to generate NH3. According to experimental and theoretical investigations, photocatalytic N2 fixation on NVs‐g‐C3N4/WO3 composites is proposed to be energetically favorable in the alternating pathway. This study offers an alternative way for the design of efficient photocatalysts for photocatalytic N2 fixation.

Carbon tungsten oxide composite cathode materials for aluminum-ion batteries

Aluminum-ion batteries use more abundant materials and suffer from fewer safety risks than lithium-ion batteries. In this work, new cathode materials for Al-ion batteries were synthesized and tested. WO3, carbon materials, and WO3-carbon composite were prepared by sol-gel and chemical vapor deposition methods. These materials differ in microstructure and other physicochemical properties and the possibility of using them as cathode materials was tested. The correlation between the phase composition, structure, microstructure, electrical properties, and electrochemical performance was described based on X-ray diffraction, scanning electron microscopy, electrochemical impedance spectroscopy, and galvanostatic discharge results. WO3, Norit, and WO3/carbon core-shell composite materials exhibit the smallest average grain size in the range of tens of nanometers while materials based on potato starch carbons contain grains in the range of tens of micrometres. The highest values of the open cell voltage and capacitance of Al-ion cells were found for single-phase WO3 and Norit materials, whereas in the case of single-phase Carbon PS these parameters acquire much lower values.

Polyester‐Based Polymer Composites for Gamma Shielding Applications ‐ A Substitute for Lead

AbstractTungsten oxide (WO3) filled Isophthalic polyester based polymer composites were fabricated by open mould cast technique. The gamma shielding ability of the composites was investigated using gamma ray spectrometer for 80, 127, 356, 662, 1170 & 1332 keV gamma rays in detail and several shielding parameters were estimated to decide the shielding effectiveness of the polymer composites. The results show that, the linear attenuation coefficient increases upon adding tungsten oxide into the matrix and decreases with increase in the energy of gamma photons and is found to be maximum for 80 keV gamma rays. The half value layer thickness, tenth value layer thickness and relaxation length were found to decrease with increase in the filler Wt %, whereas, they were found to increase with increase in energy. XCOM & WinXCOM computer codes were used to estimate the electron density and Zeff of the composites theoretically. ISO+50 Wt % WO3 composite is found to be just 18 % heavy with respect to lead and show better performance than lead at 80 keV and baryte at 127 keV and is almost comparable to steel and concrete in the higher energy range. Thus, lead (Pb) can be replaced by ISO+50 Wt % WO3 composite for low energy gamma shielding applications.

Preparation and evaluation of gamma shielding properties of silicon-based composites doped with WO3 micro- and nanoparticles

This study aims to investigate the shielding properties of silicon-based WO3 composites against gamma radiation. The filler particles in micro and nano-size were prepared with a wet chemical synthesis method. Consequently, different weight percentages of micro and nano WO3 composites (5, 10, 15, 20, 30, 50, and 70 wt%) were produced. Structural and morphological characterizations of the composites were investigated using SEM and EDS analyses. Moreover, for the thermal characterization of the nanocomposites and to prove the thermal stability, TGA analysis was carried out. The results indicated that adding WO3 nanoparticles to the silicon matrix decreases the glass transition temperature of the composites. Additionally, shielding properties of the nano and micro composites were investigated using a NaI(Tl) scintillator detector at different photon energies and experimental results verified by MCNP Monte Carlo code and XCOM program. It was illustrated that, especially at lower energies, in both micro-and nanocomposites samples, by increasing the weight percentages of the filler particles, shielding abilities of the composites enhance appreciably.

Enhancing the Spectroelectrochemical Performance of WO3 Films by Use of Structure-Directing Agents during Film Growth

Thin, porous films of WO3 were fabricated by solution-based synthesis via spin-coating using polyethylene glycol (PEG), a block copolymer (PIB50-b-PEO45), or a combination of PEG and PIB50-b-PEO45 as structure-directing agents. The influence of the polymers on the composition and porosity of WO3 was investigated by microwave plasma atomic emission spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, X-ray diffraction, and gas sorption analysis. The electrochromic performance of the WO3 thin films was characterized with LiClO4 in propylene carbonate as electrolyte. To analyze the intercalation of the Li+ ions, time-of-flight secondary ion mass spectrometry, and X-ray photoelectron spectroscopy were performed on films in a pristine or reduced state. The use of PEG led to networks of micropores allowing fast reversible electrochromic switching with a high modulation of the optical transmittance and a high coloration efficiency. The use of PIB50-b-PEO45 provided isolated spherical mesopores leading to an electrochromic performance similar to compact WO3, only. Optimum characteristics were obtained in films which had been prepared in the presence of both, PEG and PIB50-b-PEO45, since WO3 films with mesopores were obtained that were interconnected by a microporous network and showed a clear progress in electrochromic switching beyond compact or microporous WO3.

Ti/TiO2/NiWO4 + WO3 composites for oxidative desulfurization and denitrogenation

The catalytic properties of Ti/TiO2/NiWO4 + WO3 composites fabricated by plasma electrolytic oxidation (PEO) of titanium in a solution containing 0.1 mol/L Na2WO4 + 0.1 mol/L CH3COOH + 0.05 mol/L Ni(CH3COO)2 were studied in model reactions of peroxide oxidation of thiophene (T), dibenzothiophene (DBT), methylphenyl sulfide (MPhS), and pyridine (Py). This paper demonstrates for the first time that such composites are promising for catalytic oxidation of both S-containing and N-containing petroleum compounds. By the example of the reaction of dibenzothiophene oxidation, the optimal reaction temperature (60 °C) and the content of hydrogen peroxide in the reaction mixture were established, and the efficiencies of the Ti/TiO2/NiWO4 + WO3 and Ti/TiO2/WO3 composites were compared to show the role of nickel in increasing their activity and stability. It was found that, with respect to organosulfur substrates, the activity of the Ti/TiO2/NiWO4 + WO3 catalyst decreases in the series: methylphenyl sulfide > dibenzothiophene > thiophene. The changes in surface morphology and elemental composition of composites after catalytic tests have been evaluated using SEM, EDS and XPS. It has been established that the use of the Ti/TiO2/NiWO4 + WO3 catalyst makes it possible to achieve a deep degree of desulfurization of the diesel fraction of petroleum feedstock (>90%).

S, N Co-Doped Carbon Dot-Functionalized WO3 Nanostructures for NO2 and H2S Detection

This paper reports the synthesis of a S, N co-doped carbon dot (C-dot)-functionalized WO3 (C(S, N)-WO3) nanostructure via a hydrothermal method, which exhibits ultrasensitivity for NO2 at the ppb level and H2S at the ppm level along with remarkable selectivity. The WO3 morphology is optimized by varying the pH (1.5–3.5) of the solution. Characterization results reveal that the surface morphology at pH 3 is superior for producing uniform nanoneedle nanostructures with high sensitivity toward NO2 and H2S. To further enhance the sensitivity and selectivity of WO3 nanoneedles, the effect of mixing of C-dots into WO3 is investigated systematically. The optimized weight of C-dots in the C(S, N)-WO3 composite is 10 mg, which exhibits sensitivity values of 2.2 to 250 ppb for NO2 and 29.5 to 100 ppm for H2S. The C(S, N)-WO3 composite material shows the highest sensitivity at an optimum substrate temperature of 150 °C, without an obvious influence of humidity up to 50% relative humidity. The limit of detection of the composite sensor is 250 ppb NO2 along with excellent repeatability and good long-term stability.