Preparation of direct Z-scheme Bi2WO6/TiO2 heterojunction by one-step solvothermal method and enhancement mechanism of photocatalytic H2 production

Direct Z-scheme Bi₂WO₆/TiO₂ heterojunction photocatalyst was prepared by one-step solvothermal method. The catalyst was characterized by XRD, TEM, XPS, UV–Vis DRS, photoluminescence spectroscopy and photoelectrochemical studies. The photocatalytic hydrogen production experiments show that Bi₂WO₆ did not generate H₂ and the H₂-production rate of TiO₂ is only 0.1 mmol⋅g⁻¹h⁻¹. The hydrogen production rate of the Bi₂WO₆/TiO₂ heterojunction photocatalyst reaches 12.9 mmol⋅g⁻¹h⁻¹, which is 129 times that of TiO₂. Compared with TiO₂, the enhanced H₂-production activity of the heterojunction catalyst can be attributed to the wider light absorption range and the efficient separation and migration of carriers at the close contact interface between Bi₂WO₆ and TiO₂. Based on the work functions of Bi₂WO₆, TiO₂ and their heterojunctions, combined with the results of electron paramagnetic resonance spectroscopy and Mott-Schottky measurements, the photocatalytic H₂ production mechanism of Z-scheme heterojunction Bi₂WO₆/TiO₂ was proposed. This work provides an easy and simple way to design a binary Z-scheme photocatalyst with efficient catalytic H₂-production activity without electron mediators.     

In situ tuning of band gap of Sn doped composite for sustained photocatalytic hydrogen generation under visible light irradiation

The significance of Sn dopant on the photocatalytic performance of Iron/Titanium nanocomposite towards photocatalytic hydrogen generation by water splitting reaction is investigated. Iron/Titanium nanocomposite modified by Sn⁴⁺ dopant acts as a suitable photocatalyst for induced visible light absorption facilitating pronounced charge separation efficiency. Various characterization techniques reveal the heterojunction formation of hematite Fe₂O₃ with anatase - rutile mixed phase of TiO₂ employing Sn doping, where Sn⁴⁺ dopant accomplishes the phase transformation of anatase to rutile, entering into the TiO₂ lattice. This extended the lifetime of photogenerated charge carriers and enhanced the quantum efficiency of the photocatalyst. The band gap of the nanocomposite is tuned to ~2.4 eV, favoring visible light absorption. A hydrogen generation activity of 1102.8 μmol, approximately five times higher than the lone system (216.5 μmol) is achieved for the 5% Sn doped system for an average of 5 h. Heterojunctions of hematite with anatase-rutile mixed phase, generated as a consequence of tin doping facilitated the enhanced hydrogen generation activity of photocatalyst.     

Photodeposition of AuNPs on metal oxides: Study of SPR effect and photocatalytic activity

Effect of photodeposition of AuNPs (gold nanoparticles) on TiO₂, CeO₂, Cu₂O and Fe₃O₄ supports has been illustrated on sacrificial donor based hydrogen evolution. The synthesized samples were characterized by diffuse reflectance spectroscopy (DRS), and transmission electron microscopy (TEM). Highest photocatalytic activity was exhibited by Au/TiO₂ followed by Au/Fe₃O₄, Au/CeO₂ and Au/Cu₂O. Au/TiO₂ under optimized conditions has shown significantly high photocatalytic activity under both UV–visible and visible radiation. Au/TiO₂ shows hydrogen evolution rate of 920 μmol h⁻¹ and 32.4 μmol h⁻¹ under UV–visible and visible radiation, respectively. Significant enhancement in hydrogen evolution rate under visible light is very encouraging and may be attributed to polydispersed nature of AuNPs wherein larger particles facilitate light absorption and the smaller function as catalytic sites. Further studies are in progress to study the influence of various parameters on photocatalytic activity of Au/TiO_2.     

Rh nanospheres anchored TaON@Ta2O5 nanophotocatalyst for efficient hydrogen evolution from photocatalytic water splitting under visible light irradiation

Rh nanospheres anchored TaON@Ta₂O₅ with shell-core structure was synthesized from in-situ Rh³⁺-doped Ta₂O₅ by one-step high-temperature ammonolysis, which exhibited efficient visible light photoactivity for H₂-evolution (39.41 μmol·g⁻¹·h⁻¹), much higher than unmodified Ta₃N₅@Ta₂O₅ (21.75 μmol·g⁻¹·h⁻¹). Rh-modifying inhibited the phase transformation from TaON to Ta₃N₅ during the nitridation process, and increased the specific surface area and active sites, and extended the optical absorption throughout visible light region due to localized surface plasmon resonance (LSPR) effect. Relative intensities of peaks at 827 cm⁻¹ for Ta–O bonds increased with increasing Rh-modifying amounts, which was beneficial to improving the stability. Notably, constructing novel Rh/TaON/Ta₂O₅ heterojunctions including a Rh/TaON Schottky junction and an n-n TaON/Ta₂O₅ mutant heterojunction facilitated photogenerated carriers directed transfer from inner to surface active sites, and decreased travel distance of charge carriers, and formed built-in electric fields to accelerating charge separation. Synergetic effects of the enhanced photocatalytic H₂-evolution activity were discussed in detail. This work provided a promising strategy to further design and develop efficient and stable Ta-based photocatalysts for solar water splitting.     

Nano cobalt oxides for photocatalytic hydrogen production

Nano structured metal oxides including TiO_2, Co₃O₄ and Fe₃O₄ have been synthesized and evaluated for their photocatalytic activity for hydrogen generation. The photocatalytic activity of nano cobalt oxide was then compared with two other nano structured metal oxides namely TiO₂ and Fe₃O₄. The synthesized nano cobalt oxide was characterized thoroughly with respect to EDX and TEM. The yield of hydrogen was observed to be 900, 2000 and 8275 μmol h⁻¹ g⁻¹ of photocatalyst for TiO₂, Co₃O₄ and Fe₃O₄ respectively under visible light. It was observed that the hydrogen yield in case of nano cobalt oxide was more than twice to that of TiO₂ and the hydrogen yield of nano Fe₃O₄ was nearly four times as compared to nano Co₃O₄. The influence of various operating parameters in hydrogen generation by nano cobalt oxide was then studied in detail.     

Surface defect and rational design of TiO2−x nanobelts/ g-C3N4 nanosheets/ CdS quantum dots hierarchical structure for enhanced visible-light-driven photocatalysis

TiO_2-x/g-C₃N₄/CdS ternary heterojunctions are fabricated through thermal polymerization-chemical bath deposition combined with in-situ solid-state chemical reduction approach. The prepared materials are characterized by X-ray diffraction, Fourier transform infrared spectra, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption-desorption, and X-ray photoelectron spectroscopy. The results show that the ternary heterojunctions are formed successfully and CdS quantum dots (QDs) and TiO₂ are anchored on surface of g-C₃N₄ nanosheets simultaneously. The visible-light-driven photocatalytic degradation ratio of Bisphenol A and hydrogen production rate are up to 95% and ∼254.8 μmol h⁻¹, respectively, which are several times higher than that of pristine TiO₂. The excellent visible-light-driven photocatalytic activity can be ascribed to the synergistic effect of TiO_2−x, g-C₃N₄ and CdS QDs which extend the photoresponse to visible light region and favor the spatial separation of photogenerated charge carriers.     

ZnIn2S4 nanosheets decorating WO3 nanorods core-shell hybrids for boosting visible-light photocatalysis hydrogen generation

We here report the fabrication of a core-shell WO₃@ZnIn₂S₄ heterostructure by an interfacial seeding growth strategy, which is implemented by direct growth of ZnIn₂S₄ nanosheets on the surface of WO₃ nanorods with forming a strong electronic interaction between two semiconductors that are beneficial for promoting the interfacial charge transfer. Systematic studies demonstrate that the WO₃@ZnIn₂S₄ nanohybrids hold superior performance for photocatalytic hydrogen generation under visible light irradiation with a production rate of 3900 μmol g⁻¹ h⁻¹. This work provides an effective approach to construct the direct Z-scheme photocatalytic systems for efficient photocatalytic hydrogen evolution, which would be significant for the design of more direct Z-scheme system for various photocatalytic applications.     

Hierarchically SrTiO3@TiO2@Fe2O3 nanorod heterostructures for enhanced photoelectrochemical water splitting

In this particular work, the fabrication of SrTiO₃@TiO₂@ Fe₂O₃ nanorod heterostructure has been demonstrated via hydrothermal growth of SrTiO₃ cubic on the rutile TiO₂ nanorod as a template and later sensitized with Fe₂O₃ for photocatalytic solar hydrogen production in a tandem photoelectrochemical cell and dye-sensitized solar cell (DSSC) module. The photocatalytic solar hydrogen production of this heterostructure was optimized by controlling the amount of Sr and Fe on the surface of photocatalyst. The details of the influencing parameters on the physicochemical and photoelectrochemical properties are discussed. It was found that the morphology and quality of the fabricated materials were greatly manipulated by the concentration of Sr and Fe. The optimized 0.025 M SrTiO₃@TiO₂@ Fe₂O₃ heterostructure exhibited a higher photoconversion efficiency with a long electron lifetime, low charge transfer resistance and large donor density at the electrode and electrolyte interface. This composite has significantly improved the photocatalytic hydrogen production, yielding 716 μmol/cm² of maximum accumulative hydrogen. These results show that morphology rendering and manipulation of energy band alignment is crucial in creating efficient heterojunctions for excellent contributions in photocatalytic applications.     

Carbon nitride quantum dots (CNQDs)/TiO2 nanoparticle heterojunction photocatalysts for enhanced ultraviolet-visible-light-driven bisphenol a degradation and H2 production

The extension of the absorption band of solar energy is an efficient strategy to dramatically enhance the application value of TiO₂. Based on this, we have prepared carbon nitride quantum dots (CNQDs)/TiO₂ nanoparticle heterojunctions by mixing TiO₂ and the as-prepared CNQDs by the simple mechanical stirring method. The synthesized CNQDs-x/TiO₂ composites were systematically characterized in term of their physicochemical properties, the performance of photocatalytic degradation of Bisphenol A, and their photocatalytic hydrogen evolution performance under stimulated sunlight. The CNQDs/TiO₂ nanoparticle exhibited a lattice spacing of 0.352 nm, assigning to the (101) crystal plane of anatase phase TiO_2. Intriguingly, the modification of TiO₂ nanoparticle with CNQDs can indeed get a narrower optical band gap of 3.02 eV, with a wider absorption range extending to visible light region and could enhance their overall photocatalytic performance over the commercially TiO₂ nanoparticles. In Addition, it was demonstrated that the ratios of CNQDs to TiO₂ exhibited obvious influence on the photocatalytic performance of the obtained composite catalysts.By contrast to the pure TiO₂, all the CNQDs-x/TiO₂ composites displayed higher photocatalytic activities, and the CNQDs-2/TiO₂ possessed the highest photocatalytic degradation capacity towards bisphenol A with a reaction rate constant 0.30 (0.17 for pure TiO₂). Meanwhile, the H₂ production rate of CNQDs-2/TiO₂ sample is about 30 μmol g⁻¹ h⁻¹ higher than that of the pure TiO₂ nanoparticles. Moreover, the photocurrent intensity of CNQDs-2/TiO₂ was about 25 times higher compared to that of pure TiO₂ nanoparticles. Therefore, our research results can provide valuable guidance for exploring high-performance photocatalytic materials.     

CuWO4 as a novel Z-scheme partner to construct TiO2 based stable and efficient heterojunction for photocatalytic hydrogen generation

Synthesis of highly efficient, stable, visible active CuWO₄ nanoparticles through a simple methodology, paves a feasible path for enhancing the efficiency of TiO₂. A novel nanocomposite of CuWO₄ NP loaded TiO₂ NR heterojunction was mounted through a direct Z-scheme mechanism. Optimized composite CWT-3, advances the photocatalytic hydrogen production rates of TiO₂ to 106.7 mmol h^?1 g^?1_cat. CuWO₄ incorporation as OEP compensates inefficiency of WO₃ and other Z-scheme combinations reported so far, on limiting the charge carrier recombination followed by the generation of a greater number of excitons. Specific amounts of catalyst loading, study on the effect of sacrificial reagents, and understanding the effect of the light source, are the three pivotal steps that helped here to hamper the density of overall back reactions. The formation of Z-scheme heterojunction was evidently confirmed on determining the position of CBM and VBM, PL and photoelectrochemical analysis. Recyclability studies further proved the stable and efficient outcomes of CWT-3 for five consecutive cycles. Based on photocatalytic activity, employing BDF by-product glycerol as an optimized sacrificial reagent serves the oxidation demands and triggered 53.26% solar to hydrogen conversion efficiency under natural sunlight irradiation.     

One-pot synthesis of Cu–TiO2/CuO nanocomposite: Application to photocatalysis for enhanced H2 production,dye degradation & detoxification of Cr (VI)

Photocatalytic hydrogen production under the visible spectrum of solar light is an important topic of research. To achieve the targeted visible light hydrogen production and improve the charge carrier utilization, bandgap engineering and surface modification of the photocatalyst plays a vital role. Present work reports the one-pot synthesis of Cu–TiO₂/CuO nanocomposite photocatalyst using green surfactant -aided -ultrasonication method. The materials characterization data reveals the TiO₂ particle size of 20–25 nm and the existence of copper in the lattice as well as in the surface of anatase TiO₂. This is expected to facilitate better optical and surface properties. The optimized photocatalyst shows enhanced H₂ production rate of 10,453 μmol h⁻¹ g⁻¹ of the catalyst which is 21 fold higher than pure TiO₂ nanoparticles. The photocatalyst was tested for degradation of methylene blue dye (90% in 4 h) in aqueous solution and photocatalytic reduction of toxic Cr⁶⁺ ions (55% in 4 h) in aqueous solution. A plausible mechanistic pathway is also proposed.     

Evaluation of in-situ formed La2O3–TiO2–La2O2CO3 nanocomposite photocatalyst for H2 production

The photocatalytic evolution of H₂ over La₂O₃ decorated TiO₂ catalyst was examined under solar light. It was observed that during the course of the reaction, the transformation of La₂O₃/TiO₂ into La₂O₃–TiO₂–La₂O₂CO₃ occurred and these species effectively suppressed electron-hole pair recombination by forming electron trapping centres on the surface, resulting in an increased visible light absorption and improved H₂ yield. The 2 wt%La₂O₃/TiO₂ nanocomposite demonstrated better H₂ yield (～8.76 mmol (g_cat)^?1) than the bare TiO₂ (～1.1 mmol (g_cat)^?1). The catalyst was stable even after several consecutive recycles with no substantial loss of hydrogen production rate. The H₂ rates were correlated with the physicochemical characteristics of the catalysts examined by BET–SA, H₂-TPR, XRD, UV-DRS, Raman spectroscopy, FTIR, HRTEM, EPR and PL spectroscopy.     

Mesoporous g-C3N4/Zn–Ti LDH laminated van der Waals heterojunction nanosheets as remarkable visible-light-driven photocatalysts

Mesoporous g-C₃N₄/Zn–Ti layered double hydroxide (LDH)-laminated van der Waals heterojunction nanosheets were prepared by a facile one-step in situ hydrothermal method. Due to the strong electrostatic interactions between the positively charged Zn–Ti LDH and negatively charged g-C₃N₄ nanocrystal, a laminated van der Waals heterostructure was successfully formed between Zn–Ti LDH and g-C₃N₄. The mesoporous g-C₃N₄/Zn–Ti LDH-laminated van der Waals heterojunction, which had a narrow bandgap of 2.41 eV extended the photoresponse to the visible light region. The obtained heterojunctions showed excellent visible-light-driven photocatalytic performance for the complete removal of ceftriaxone sodium (up to ∼97%) and a high hydrogen production rate (∼161.87 μmol h⁻¹ g⁻¹). This was mainly attributed to the formation of the laminated van der Waals heterojunctions, which favoured charge separation and the absorption of visible light, and the mesoporous structure, which provided more surface active sites. This facile strategy for preparing mesoporous g-C₃N₄/Zn–Ti LDH-laminated van der Waals heterojunctions offers new insights for the fabrication of high-performance van der Waals heterojunction photocatalytic materials.     

Ultrathin hematite films deposited layer-by-layer on a TiO2 underlayer for efficient water splitting under visible light

Ultrathin hematite (α-Fe₂O₃) film deposited on a TiO₂ underlayer as a photoanode for photoelectrochemical water splitting was described. The TiO₂ underlayer was coated on conductive fluorine-doped tin oxide (FTO) glass by spin coating. The hematite films were formed layer-by-layer by repeating the separated two-phase hydrolysis-solvothermal reaction of iron(III) acetylacetonate and aqueous ammonia. A photocurrent density of 0.683 mA cm⁻² at +1.5 V vs. RHE (reversible hydrogen electrode) was obtained under visible light (>420 nm, 100 mW cm⁻²) illumination. The TiO₂ underlayer plays an important role in the formation of hematite film, acting as an intermediary to alleviate the dead layer effect and as a support of large surface areas to coat greater amounts of Fe₂O₃. The as-prepared photoanodes are notably stable and highly efficient for photoelectrochemical water splitting under visible light. This study provides a facile synthesis process for the controlled production of highly active ultrathin hematite film and a simple route for photocurrent enhancement using several photoanodes in tandem.     

Experimental evaluation of Pt/TiO2/rGO as an efficient HER catalyst via artificial photosynthesis under UVB & visible irradiation

The study investigated the synergistic effects of rGO and Pt over TiO₂ for the HER via artificial photosynthesis under UVB and visible light irradiation. The introduction of glycerol and industrial wastewater to the system as sacrificial reductants signifies that the major reaction pathway is photocatalytic partial water splitting. The material characterizations revealed successful heterojunction formation and provided insight into chemistry behind the activity of the photocatalysts. Amongst various combinations of rGO on TiO₂, 1GNT exhibited an HER yield five times that of bare TiO₂ under UVB light. Addition of Pt led to the formation of a strong Schottky barrier at the heterojunction and consequently boosted HER performance. 1P0.5 GT presented the highest of 28.5 mmol g⁻¹ h⁻¹ with glycerol and 9.6 mmol g⁻¹ h⁻¹ with wastewater under UVB light respectively. For both binary and ternary photocatalysts, the HER performances dwindled under visible light irradiation, accentuating the insufficient activation of the TiO₂. In addition, 1PT outperformed all the other photocatalysts thereby elucidating the impression that rGO and Pt does not work well together in enhancing HER despite quenching the exciton recombination rate of TiO₂ significantly. The role of pH in the synthesis and the experiments has been discussed. Finally, the underlying mechanisms in the photodeposition and photoreformation have been proposed.     

Effect of rGO on Fe2O3–TiO2 composite incorporated NiP coating for boosting hydrogen evolution reaction in alkaline solution

Fe₂O₃–TiO₂ composite incorporated NiP coating is a known promising catalytic coating for electrocatalytic Hydrogen Evolution Reaction (HER). It is explored in the present study that the activity of the coating can be enhanced by incorporation of rGO. The Fe₂O₃–TiO₂/rGO, electrocatalyst is synthesized by a facile hydrothermal method. Various compositions of the Fe₂O₃–TiO₂/rGO incorporated NiP coatings on mild steel substrate are developed by a chemical reduction method. The developed Fe₂O₃–TiO₂/rGO composite coating exhibits effective hydrogen evolution reaction activity with a Tafel slope of 98 mV dec⁻¹ and a low overpotential of 96 mV at a current density of 10 mA cm⁻². The hydrogen evolution reaction mechanism comprises of Volmer (adsorption of Hydrogen atom) followed by Heyrovskii (reduction to H₂). The enhanced catalytic activity by the incorporation of rGO into the coating is due to three dimensional projections of nano Fe₂O₃–TiO₂ on the folded surface of rGO. It effectively enhances the electrochemically active surface area of the coated electrode. The electrode is highly stable during alkaline HER. These results reveal that Fe₂O₃–TiO₂/rGO can be treated as an effective electrocatalyst during HER from alkaline solutions. The conclusions pave the way for exploration of new similar catalysts for other applications.     

A nanoreactor based on SrTiO3 coupled TiO2 nanotubes confined Au nanoparticles for photocatalytic hydrogen evolution

A TiO₂ nanotube-based nanoreactor was designed and fabricated by facile two steps synthesis: firstly, hydrothermal synthesized SrTiO₃ was deposited on TiO₂ nanotubes (TiO₂NTs). Secondly, the Au nanoparticles (NPs) were encapsulated inside the TiO₂NTs followed by vacuum-assisted impregnation. The as-synthesized composites were characterized using Transmission electron microscopy (TEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Photoluminescence spectra (PL) and Ultraviolet–visible absorption spectroscopy (UV–vis). The photocatalytic performance was evaluated by the hydrogen evolution reaction. The results revealed that the SrTiO₃ modified TiO₂NTs confined Au NPs (STO-TiO₂NTs@Au) achieved an enhanced hydrogen evolution rate at 7200 μmol h⁻¹ g⁻¹, which was 2.2 times higher than that of bald TiO₂NTs@Au at 3300 μmol h⁻¹ g⁻¹. The improved photocatalytic activity could be attributed to the synergistic effect of the electron-donating of SrTiO₃ and TiO₂NTs confinement. The as-designed nanoreactor structure provides an example of efficient carriers' separation photocatalyst.     

Enhanced photocatalytic hydrogen evolution from reduced graphene oxide-defect rich TiO2-x nanocomposites

Solar-driven photocatalytic hydrogen generation by splitting water molecules requires an efficient visible light active photocatalyst. This work reports an improved hydrogen evolution activity of visible light active TiO_2-x photocatalyst by introducing reduced graphene oxide via an eco-friendly and cost-effective hydrothermal method. This process facilitates graphene oxide reduction and incorporates intrinsic defects in TiO₂ lattice at a one-pot reaction process. The characteristic studies reveal that RGO/TiO_2-x nanocomposites were sufficiently durable and efficient for photocatalytic hydrogen generation under the visible light spectrum. The altered band gap of TiO_2-x rationally promotes the visible light absorption, and the RGO sheets present in the composites suppresses the electron-hole recombination, which accelerates the charge transfer. Hence, the noble metal-free RGO/TiO_2-x photocatalyst exhibited hydrogen production with a rate of 13.6 mmol h^?1g^?1_cat. under solar illumination. The appreciable photocatalytic hydrogen generation activity of 947.2 μmol h^?1g^?1_cat with 117 μAcm^?2 photocurrent density was observed under visible light (>450 nm).     

Fabrication of a ternary PANI@Fe3O4@CFs nanocomposite as a high performance electrode for solid-state supercapacitors

In this work, a solid-state high performance supercapacitor is fabricated based on a ternary polyaniline@Fe₃O₄@carbon fibers nanocomposite. To prepare the polyaniline@Fe₃O₄@carbon fibers electrodes, a two-step method including electrophoretic deposition of Fe₃O₄ nanoparticles on carbon fibres followed by an in situ polymerization process of polyaniline is utilized. The results show that the polyaniline@Fe₃O₄@carbon fibers nanocomposite with a layer by layer microstructure is successfully formed. The fabricated nanocomposite represents a specific surface area of 3.12 m² g⁻¹. The electrochemical measurements in a three-electrode configuration reveals a high specific capacitance of 245.5 F g⁻¹ at 0.5 A g⁻¹ and an excellent cycle stability (82.44% after 1000 cycle) of the polyaniline@Fe₃O₄@carbon fibers electrode. The as-fabricated solid-state supercapacitor based on the polyaniline@Fe₃O₄@carbon fiber nanocomposite cloth with a surface area of 25 cm² powers up a blue light-emitting diode for 4 min and delivers a high energy density of 78.6 Wh.kg⁻¹ at a power density of 1047.5 W kg⁻¹.     

Hierarchical TiO2 spheroids decorated g-C3N4 nanocomposite for solar driven hydrogen production and water depollution

A novel hierarchical TiO₂ spheroids embellished with g-C₃N₄ nanosheets has been successfully developed via thermal condensation process for efficient solar-driven hydrogen evolution and water depollution photocatalyst. The photocatalytic behaviour of the as-prepared nanocomposite is experimented in water splitting and organic pollutant degradation under solar light irradiation. The optimal ratio of TiO₂ spheroids with g-C₃N₄ in the nanocomposite was found to be 1:10 and the resulting composite exhibits excellent photocatalytic hydrogen production of about 286 μmol h^?1g^?1, which is a factor of 3.4 and 2.3 times higher than that of pure TiO₂ and g-C₃N₄, respectively. The outstanding photocatalytic performance in this composite could be ascribed as an efficient electron-hole pair's separation and interfacial contact between TiO₂ spheroids with g-C₃N₄ nanosheets in the formed TiO₂/g-C₃N₄ nanocomposite. This work provide new insight for constructing an efficient Z-scheme TiO₂/g-C₃N₄ nanocomposites for solar light photocatlyst towards solar energy conversion, solar fuels and other environmental applications.