Effects of calcination temperatures on photocatalytic activity of SnO2/TiO2 composite films prepared by an EPD method

Wastewater Treatment Using High-Performance In Situ Formed Double-Heterojunction Janus Photocatalyst Microparticles Shaped via a Microfluidic Device

In this work, a heterogeneous photocatalysis system is fabricated for treating wastewater containing organic dyes and pharmaceutical substances. Double-heterojunction Janus photocatalysts are formed on the surface of size-tunable polydimethylsiloxane (PDMS) microparticles shaped via simple and low-cost coflow microfluidic devices. Ag0/Ag0-TiO2/TiO2 Janus-like photocatalysts are synthesized on the surface of porous PDMS microparticles as the support in which the metal-semiconductor heterojunction of Ag0/Ag0-TiO2 and the second heterojunction of Ag0-TiO2/TiO2 are created in situ, leading to the formation of Ag0/Ag0-TiO2/TiO2@PDMS photocatalysis systems. To form the heterojunctions on the PDMS surface, the polymer chain etching method is employed as a desired strategy to have half of the TiO2 nanoparticles on the surface of microparticles, which are treated by a Ag source. Using salt additives and the etching method, PDMS microparticles are made porous, providing more surface area for photoreactions. Surprisingly, the highest decomposition efficiencies of 94.4 and 91.1% are achieved for rhodamine B(RhB) and tetracycline (TC), respectively, under visible light for 60 min pH 11, a light source at a distance of 2 cm, 5 mM AgNO3, 10 wt % TiO2, 7 wt % NaCl, and 20 gm/L photocatalyst, which are conditions that result in the best performance for RhB degradation. Regarding the stability of the photocatalysts, no significant change is observed in the performance after five cycles.

Composite Photocatalysts with Fe, Co, and Ni Oxides on Supports with Tetracoordinated Ti Embedded into Aluminosilicate Gel during Zeolite Y Synthesis

Ti-aluminosilicate gels were used as supports for the immobilization of Fe, Co, and Ni oxides (5%) by impregnation and synthesis of efficient photocatalysts for the degradation of β-lactam antibiotics from water. Titanium oxide (1 and 2%) was incorporated into the zeolite network by modifying the gel during the zeolitization process. The formation of the zeolite Y structure and its microporous structure were evidenced by X-ray diffraction and N2 physisorption. The structure, composition, reduction, and optical properties were studied by X-ray diffraction, H2-TPR, XPS, Raman, photoluminescence, and UV-Vis spectroscopy. The obtained results indicated a zeolite Y structure for all photocatalysts with tetracoordinated Ti4+ sites. The second transitional metals supported by the post-synthesis method were obtained in various forms, such as oxides and/or in the metallic state. A red shift of the absorption edge was observed in the UV-Vis spectra of photocatalysts upon the addition of Fe, Co, or Ni species. The photocatalytic performances were evaluated for the degradation of cefuroxime in water under visible light irradiation. The best results were obtained for iron-immobilized photocatalysts. Scavenger experiments explained the photocatalytic results and their mechanisms. A different contribution of the active species to the photocatalytic reactions was evidenced.

Morphological analysis and grain size distribution of SnO2 nanoparticles via digital image processing across diverse calcination temperatures

This study presents a comprehensive image analysis of the SnO2 nanoparticles synthesised through calcination at diverse temperatures, which enables an estimation of grain size distribution (GSD) from field-emission scanning electron microscopy (FE-SEM) images. Even though FE-SEM images could provide us with a lot of information about sample differences, we can learn more and perform a more accurate analysis of them by using quantitative data obtained by our image processing application. The digital image processing techniques used in this research provide a detailed analysis of the nanoparticles' size and shape, enabling a deeper understanding of their unique characteristics. The results reveal the significant impact of calcination temperature on the morphology of the nanoparticles, with changes in grain size and grain size distribution observed at varying temperatures.

Controlled Phase Transformation and Crystal Growth of Titanium Dioxide from Anatase/Silica Core/Shell Particles

Anatase/silica core/shell particles were prepared by the hydrolysis and condensation of tetraethyl orthosilicate on anatase particles with the sizes of 9, 22, and 111 nm, respectively. The thickness of the silica layer was designed from ca. 3 to 14 nm by repeating the coating procedure on anatase with a particle size of 22 nm. By the heat treatment at 1000 °C, though the pristine anatase particles transformed to rutile, anatase remained for the silica-coated particles. Anatase particles (111 nm) transformed to rutile upon heating at 1100 °C, while the transformation was not observed for the smaller particles (9 and 22 nm). With the increase of the silica thickness to 14 nm, anatase did not transform to rutile even after heating at 1150 °C, while resulting in varied compositions of anatase and rutile after heating at 1200 °C. The crystal growth of anatase and rutile was also suppressed for the silica-coated particles compared with that seen for pristine anatase. Thus, the thermal transformation and crystal growth of titania were controlled by the coating with silica, and the effects were shown to affect the coating.

New generation advanced nanomaterials for photocatalytic abatement of phenolic compounds

Nowadays, organic pollutants create severe problems worldwide. Phenolic compounds are the harmful pollutants that are developed from industrial effluents, thus causing several environmental problems. Low-cost materials show good potential capabilities for removal of phenolic compounds but are not so effective, so modification is required. New generation nanocatalysts are thought to be excellent for phenol removal. Removal of phenolic pollutants by photodegradation may lead to the decrement of these problematic groups. In this review, (i) a new generation of catalysts for the removal of phenolic compounds is discussed, (ii) nanocatalysts for photodegradation processes, and (iii) the mechanisms involved in photodegradation processes are also discussed. It is noticeable from the analysis that new generation catalysts for photodegradation processes have been demonstrated for high removal abilities of irrefutable phenolic compounds. Finally, future perspectives are also given in this article for the further development of next-generation catalysts.

Role of NiO Nanoparticles in Enhancing Structure Properties of TiO2 and Its Applications in Photodegradation and Hydrogen Evolution

Pure and modified mesoporous TiO2 nanoparticles with different loadings of NiO (3-20.0 wt %) were prepared through the surfactant-assisted sol-gel approach with the use of cetyltrimethylammonium bromide as a template. The optical and structural properties of different samples were examined using N2 adsorption-desorption analysis, energy-dispersive spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis spectroscopy, Fourier transform infrared spectroscopy, and photoluminescence (PL) spectroscopy. X-ray diffraction results confirmed the insertion of Ni2+ into the lattice of TiO2, and the crystallite size reduced remarkably after the addition of NiO. The diffuse reflectance spectroscopy spectra displayed obvious red shift in the absorption edges, and new absorption bands appeared in the visible region when NiO was added, which indicates the formation of surface defects and oxygen vacancies. The optical band gap of TiO2 reduced sharply when the contents of NiO were increased. The increase in the surface defects as well as oxygen vacancies were examined using PL spectroscopy. The photocatalytic performance of the as-synthesized samples was investigated over photodegradation of brilliant green (BG) and phenol and hydrogen generation under visible light. 10% NiO/TiO2 exhibited the highest photocatalytic efficiency. The photocatalytic activity was improved due to the creation of a p-n junction at the interface of NiO/TiO2, which efficiently promotes the separation of photogenerated electron/hole pairs and consequently enhances its photodegradation activity. According to the photocatalytic activity results, NiO contents were considered one of the most important factors affecting the photodegradation of BG and phenol and H2 evolution. Also, we discussed the mechanism of photodegradation, mineralization (total organic carbon), and photocatalytic reaction kinetics of BG and phenol.

Original Approach to Synthesize TiO2/ZnO Hybrid Nanosponges Used as Photoanodes for Photoelectrochemical Applications

In the present work, TiO2/ZnO hybrid nanosponges have been synthesized for the first time. First, TiO2 nanosponges were obtained by anodization under hydrodynamic conditions in a glycerol/water/NH4F electrolyte. Next, in order to achieve the anatase phase of TiO2 and improve its photocatalytic behaviour, the samples were annealed at 450 °C for 1 h. Once the TiO2 nanosponges were synthesized, TiO2/ZnO hybrid nanosponges were obtained by electrodeposition of ZnO on TiO2 nanosponges using different temperatures, times, and concentrations of zinc nitrate (Zn(NO3)2). TiO2/ZnO hybrid nanosponges were used as photoanodes in photoelectrochemical water splitting tests. The results indicate that the photoelectrochemical response improves, in the studied range, by increasing the temperature and the Zn(NO3)2 concentration during the electrodeposition process, obtaining an increase in the photoelectrochemical response of 141% for the TiO2/ZnO hybrid nanosponges electrodeposited at 75 °C with 10 mM Zn(NO3)2 for 15 min. Furthermore, morphological, chemical, and structural characterization was performed by Field Emission Scanning Electron Microscopy (FE-SEM) with Energy Dispersive X-Ray spectroscopy (EDX), Raman Confocal Laser Spectroscopy, X-Ray Photoelectron Spectroscopy (XPS), and Grazing Incidence X-Ray Diffraction (GIXRD).

Advanced Photocatalysts Based on Conducting Polymer/Metal Oxide Composites for Environmental Applications

Photocatalysts provide a sustainable method of treating organic pollutants in wastewater and converting greenhouse gases. Many studies have been published on this topic in recent years, which signifies the great interest and attention that this topic inspires in the community, as well as in scientists. Composite photocatalysts based on conducting polymers and metal oxides have emerged as novel and promising photoactive materials. It has been demonstrated that conducting polymers can substantially improve the photocatalytic efficiency of metal oxides owing to their superior photocatalytic activities, high conductivities, and unique electrochemical and optical properties. Consequently, conducting polymer/metal oxide composites exhibit a high photoresponse and possess a higher surface area allowing for visible light absorption, low recombination of charge carriers, and high photocatalytic performance. Herein, we provide an overview of recent advances in the development of conducting polymer/metal oxide composite photocatalysts for organic pollutant degradation and CO2 conversion through photocatalytic processes.

Band offset in semiconductor heterojunctions

Semiconductor heterojunctions are widely applied in solid-state device applications, including semiconductor lasers, solar cells, and transistors. In photocatalysis they are of interest due to their capability to hinder charge carriers' recombination. A key role in the performance of heterojunctions is that of the alignment of the band edges of the two units composing the junction. In this work, we compare the performances of three widely applied approaches for the simulation of semiconductors heterostructures, based on density functional theory calculations with hybrid functionals. We benchmark the band offsets of ten semiconductors heterostructures for which experimental values are available: AlP/GaP, AlP/Si, AlAs/GaAs, AlAs/Ge, GaAs/Ge, GaP/Si, ZnSe/Ge, ZnSe/AlAs, ZnSe/GaAs, and TiO₂/SrTiO₃. The methods considered are (i) the alternating slabs junction (ASJ), (ii) the surface terminated junction (STJ), and (iii) the independent units (IU) approach. Moreover, two different ways to determine a common reference have been considered, (i) the plane averaged electrostatic potential, and (ii) the energy of the core levels. Advantages, drawbacks and overall performances of each method are discussed. The results suggest that the accuracy in the estimation of the band offsets is ∼0.2 eV when the ASJ method is applied. The STJ approach provides a similar accuracy, while the neglection of any interface effect, as in the IU method, provides only a qualitative estimate of the band offset and can result in significant deviations from the experiment.

Tuning wall thickness of TiO2 microtubes for an enhanced photocatalytic activity with thickness-dependent charge separation efficiency

TiO₂ microtubes with tunable wall thickness have been synthesized by a one-step electrospinning method linked with a calcination process. The wall thickness of TiO₂ microtubes can be easily tuned by altering the dosage of liquid paraffin. The influence of the thickness on the light-harvesting ability and separation efficiency of the photogenerated carriers was studied using ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy, photoluminescence emission spectroscopy, and photocurrent density measurements. Results show that TiO₂ microtubes with an appropriate thickness exhibit enhanced light scattering effect, UV-vis light-harvesting ability, charge separation efficiency, and photocatalytic performance. The degradation rates of rhodamine B and 2,4-dinitrophenol by using TiO₂ microtubes synthesized at a dosage of 0.14 g/mL liquid paraffin are 99.9% within 60 min and 97.8% within 40 min, respectively, which are higher than most of the reported values. All these results suggest that our work provides an ideal strategy for adjusting the wall thickness of TiO₂ microtubes and new approach to enhance the photocatalytic performance of TiO₂.

Co3O4-Ag photocatalysts for the efficient degradation of methyl orange

In this paper, a series of Co3O4-Ag photocatalysts with different Ag loadings were synthesized by facile hydrothermal and in situ photoreduction methods and fully characterized by XRD, SEM, TEM, FTIR spectroscopy, XPS, UV-vis and PL techniques. The catalysts were used for the degradation of methyl orange (MO). Compared with the pure Co3O4 catalyst, the Co3O4-Ag catalysts showed better activity; among these, the Co3O4-Ag-0.3 catalyst demonstrated the most efficient activity with 96.4% degradation efficiency after 30 h UV light irradiation and high degradation efficiency of 99.1% after 6 h visible light irradiation. According to the corresponding dynamics study under UV light irradiation, the photocatalytic efficiency of Co3O4-Ag-0.3 was 2.72 times higher than that of Co3O4 under identical reaction conditions. The excellent photocatalytic activity of Co3O4-Ag can be attributed to the synergistic effect of strong absorption under UV and visible light, reduced photoelectron and hole recombination rate, and decreased band gap due to Ag doping. Additionally, a possible reaction mechanism over the Co3O4-Ag photocatalysts was proposed and explained.

Construction of Ag-modified TiO2/ZnO heterojunction nanotree arrays with superior photocatalytic and photoelectrochemical properties

The work involves the preparation of TiO₂/ZnO heterojunction nanotree arrays by a three-step: hydrothermal, sol–gel, and secondary hydrothermal method, and then modification of Ag quantum dots (QDs).

Attaching titania clusters of various size to reduced graphene oxide and its impact on the conceivable photocatalytic behavior of the junctions-a DFT/D + U and TD DFTB modeling

DFT/D  +  U and density functional based tight binding (DFTB) molecular modeling was used to investigate the role of the structural, electronic and optical properties of reduced graphene oxide surface (r-GO), hybridized with hydrated TiO₂ moieties of various size, ranging from small molecular Ti₂O₄ clusters into extended Ti₄₃O₈₆ rutile type nanocrystals of ~5 nm diameter. The calculated adhesion energies, varying from  -5.048 eV (r-GO|Ti₂O₄), -12.159 eV (r-GO|Ti₅O₁₀), -18.499 eV (r-GO|Ti₁₅O₃₀) to  -42.484 eV (r-GO|Ti₄₃O₈₆), indicate high stability of these composites. It was shown that electronic interactions at the r-GO|(1 1 0)TiO₂ interface give rise to net charge flow from the r-GO substrate towards the TiO₂ moieties, analyzed in terms of the partial charge density 3D plots and an interfacial dipole moment formation. The DOS structure of the composites was calculated by means of the time dependent DFTB approach, and the position and composition of the VB and CB edges, along with the presence of weak mid-gap 2p  C states originating from the intact graphene-like patches in the r-GO substrate were discussed in detail in the context of conceivable photocatalytic activity of the composites. The constructed band alignment diagram implies formation of the staggered type II scheme, with the electric field offset that is sensitive to the titania cluster size. In the case of the nano-reticular TiO₂, where only a fraction of the Ti atoms is engaged in the Ti-O-C linkers formation, recombination of the photogenerated charges is inhibited owing to favorable spatial separation effect. For small molecular TiO₂ clusters with all Ti cations anchored to the r-GO layer fast cross-relaxation quenches the beneficial interfacial charge separation effect, since the strong hybridization of the oxygen and carbon states provides a convenient pathway for the efficient electronic coupling between the CB edge states of r-GO and the VB edge states of the TiO₂ moieties. A phenomenological model of the molecular r-GO|Ti₂O₄ and the reticular r-GO|Ti₄₃O₈₆ composites was constructed in account for different photocatalytic behavior of both junctions.

Electrophoretic deposition of photocatalytic materials

Powdered photocatalytic materials have been successfully applied for the degradation of organic and inorganic pollutants as well as for hydrogen production and CO₂ photo-reduction. However, the development of strategies for the preparation of photoactive coatings is a hot topic since it is a promising step for its use in photocatalytic reactors on an industrial scale. Electrophoretic deposition is a versatile technique capable to produce coatings of nanoparticles at a relative low cost and with an excellent quality and control of the deposited material. This work summarizes the fundamental aspects of the electrophoretic deposition process, as well as the latest contributions in the deposition of several photocatalytic materials including TiO₂ and other UV-photocatalysts like ZnO, ZnS, SrTiO₃ and PbMoO₄ in addition to visible-light-driven photocatalysts such as Bi₂O₃, CdS, CdSe, g-C₃N₄, among others. Furthermore, the morphological features of the coatings along with the repercussion in the photocatalytic performance are issues discussed in the present review, based on the effect of the multiple parameters of the electrophoretic process such as the applied voltage, the deposition time, the inter-electrode distance, the concentration of the particles, the solvents and additives.

Analogous crystal orientation for immobilizing rGO/ZrO2/Ag3PO4 nanocomposite on a fluorine-doped tin oxide substrate

Immobilization of nanocomposites without compromising their photocatalytic performance is a challenging task. Here, we report a new method that utilizes analogous crystal orientations and similarities in interplanar spacings for photocatalyst immobilization. The photocatalyst rGO/ZrO₂/Ag₃PO₄ was synthesized using a green hydrothermal method. A primary layer of ZrO₂ and a secondary layer of rGO/ZrO₂/Ag₃PO₄ composite were deposited on a fluorine-doped tin oxide (FTO) substrate. The analogous crystal orientation and interplanar spacing of ZrO₂ between the two layers resulted in composite immobilization on the FTO substrate. X-ray diffraction analysis confirmed that ZrO₂ growth occurred along the same crystal planes in both layers. The film exhibited a low band gap energy (2.6 eV) and excellent light absorption. Photocatalytic performance achieved 92% para-nitrophenol degradation in 150 min. The degradation performance of this immobilization method was 43% higher than those of rGO/ZrO₂/Ag₃PO₄ films deposited with conventional binder approaches. The quantum yield of the system was 3.46 × 10^-5 molecules·photon^-1. Finally, a figure of merit based on different parameters was determined and compared with previous results to assess the practicality of this system.

Photocatalytic degradation of diclofenac using TiO2-SnO2 mixed oxide catalysts

The complex nature of diclofenac limits its biological degradation, posing a serious threat to aquatic organisms. Our present work aims to eliminate diclofenac from wastewater through photocatalytic degradation using TiO₂-SnO₂ mixed-oxide catalysts under various operating conditions such as catalyst loading, initial diclofenac concentration and initial pH. Different molar ratios of Ti-Sn (1:1, 5:1, 10:1, 20:1 and 30:1) were prepared by the hydrothermal method and were characterized. The results indicated that addition of Sn in small quantity enhances the catalytic activity of TiO₂. Energy Band gap of the TiO₂-SnO₂ catalysts was found to increase with an increase in Tin content. TiO₂-SnO₂ catalyst with a molar ratio of 20:1 was found to be the most effective when compared to other catalysts. The results suggested that initial drug concentration of 20 mg/L, catalyst loading of 0.8 g/L and pH 5 were the optimum operating conditions for complete degradation of diclofenac. Also, the TiO₂-SnO₂ catalyst was effective in complete mineralization of diclofenac with a maximum total organic carbon removal of 90% achieved under ultraviolet irradiation. The repeatability and stability results showed that the TiO₂-SnO₂ catalyst exhibited an excellent repeatability and better stability over the repeated reaction cycles. The photocatalytic degradation of diclofenac resulted in several photoproducts, which were identified through LC-MS.

Preparation of a New Type of Black TiO2 under a Vacuum Atmosphere for Sunlight Photocatalysis

Black TiO₂ as a solar-driven photocatalyst has attracted enormous attention from scientists and engineers in water and wastewater treatment field. Most of the methods used for the preparation of black TiO₂ are thermal treatment under a hydrogen atmosphere. Nevertheless, it is well known that working with hydrogen is not safe and needs special maintenance. Here, for the first time, we prepared black TiO₂ by sintering P25 pellets at different temperatures (500-800 °C) under a vacuum atmosphere that showed the same performance with the prepared black TiO₂ under a hydrogen atmosphere. The samples were characterized by X-ray diffraction, Raman spectra field emission scanning electron microscopy, transmission electron microscopy, electron paramagnetic resonance, X-ray photoelectron spectroscopy, and ultraviolet-visible deep resistivity sounding techniques. The differences between the formation of oxygen vacancy density and color turning in sintered powder and pellet were also studied. The results showed that the color of the P25 powder became darker after sintering but not completely turning to black, whereas the P25 pellets completely turned black after sintering. The resultant black TiO₂ was used for the photocatalytic degradation of the acetaminophen (ACE) in aqueous solution under AM 1.5G solar light illumination; it was found that the P25 pellet sintered in 500 °C had the highest photocatalytic performance for ACE degradation under AM 1.5G solar light illumination. The photocatalytic activity of prepared black TiO₂ under vacuum and hydrogen atmospheres was also compared together; the results showed that photocatalytic activities of both samples were so close together. The existence of the oxygen vacancy after 6 months and long and short-term stability (by application for photocatalytic degradation of ACE in an aqueous solution) of the black TiO₂ pellets was also studied; the results showed that the TiO₂ pellets in aqueous phase had acceptable stability.

Hybrid BiOBr/UiO-66-NH2 composite with enhanced visible-light driven photocatalytic activity toward RhB dye degradation

Metal–organic framework (MOFs) based composites have received more research interest for photocatalytic applications during recent years. In this work, a highly active, visible light photocatalyst BiOBr/UiO-66-NH₂ hybrid composite was successfully prepared by introducing various amounts of UiO-66-NH₂ with BiOBr through a co-precipitation method. The composites were applied for the photocatalytic degradation of RhB (rhodamine B) dye. The developed BiOBr/UiO-66-NH₂ composites exhibited higher photocatalytic activity than the pristine material. In RhB degradation experiments the hybrid composite with 15 wt% of UiO-66-NH₂ shows degradation efficiency conversion of 83% within two hours under visible light irradiation. The high photodegradation efficiency of BUN-15 could be ascribed to efficient interfacial charge transfer at the heterojunction and the synergistic effect between BiOBr/UiO-66-NH₂. In addition, an active species trapping experiment confirmed that photo-generated hole⁺ and O₂⁻ radicals are the major species involved in RhB degradation under visible light.

Metal–organic framework (MOFs) based composites have received more research interest for photocatalytic applications during recent years.

Electrically bioactive coating on Ti with bi-layered SnO2–TiO2 hetero-structure for improving osteointegration

SnO₂–TiO₂ surface with the bi-layered structure on Ti provides internal electric stimulation to promote osteointegration of implant.

Photocatalytic efficiency of Fe2O3/TiO2 for the degradation of typical dyes in textile industries: Effects of calcination temperature and UV-assisted thermal synthesis

The inadequate management practices in industrial textile effluents have a considerable negative impact on the environment and human health due to the indiscriminate release of dyes. Photocatalysis is one of the diverse advance oxidation processes (AOPs) and titanium dioxide (TiO₂) is recognized for its high oxidation and reduction power. A composite photocatalyst of Fe₂O₃/TiO₂ is synthesized using different mass ratios of Fe:TiO₂ to improve its photoactivity. The composite photocatalyst is calcined at 300-900 °C. Their photocatalytic activity for the degradation of Congo red (CR) and methyl orange (MO) is investigated by total organic carbon (TOC) analysis. The formation and characterization of the as-prepared composite are studied by scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS). The effect of calcination temperature on the composite Fe₂O₃/TiO₂ photocatalyst is investigated using Fourier transform infrared spectroscopy (FTIR). The photocatalytic activity and the phase conversion are studied by X-ray diffraction (XRD). The specific surface area of photocatalysts at different calcination temperatures is investigated based on Brunauer-Emmett-Teller (BET) surface area analysis. Results show that at an optimum calcination temperature of 300 °C for the photocatalyst preparation, the specific surface area is maximum and the photocatalyst has the highest photoactivity. Thus, the degradation of organic materials reaches 62.0% for MO and 46.8% for CR in the presence of Fe₂O₃/TiO₂ (0.01 w:w Fe:TiO₂) calcined at 300 °C with the highest specific surface area (98.73 m²/g). The transformation of TiO₂ from anatase to rutile is facilitated by high temperature and high concentration of iron while high crystallization and particle size increase occur. An optimum calcination temperature of 300 °C is found at which the degradation of typical dyes in textile industries is maximum.

Heterojunction Photocatalysts

Semiconductor-based photocatalysis attracts wide attention because of its ability to directly utilize solar energy for production of solar fuels, such as hydrogen and hydrocarbon fuels and for degradation of various pollutants. However, the efficiency of photocatalytic reactions remains low due to the fast electron-hole recombination and low light utilization. Therefore, enormous efforts have been undertaken to solve these problems. Particularly, properly engineered heterojunction photocatalysts are shown to be able to possess higher photocatalytic activity because of spatial separation of photogenerated electron-hole pairs. Here, the basic principles of various heterojunction photocatalysts are systematically discussed. Recent efforts toward the development of heterojunction photocatalysts for various photocatalytic applications are also presented and appraised. Finally, a brief summary and perspectives on the challenges and future directions in the area of heterojunction photocatalysts are also provided.

Photocatalytic properties of Pd/TiO2 nanosheets for hydrogen evolution from water splitting

Pd/TiO₂ nanosheet catalysts were successfully prepared and used in the photocatalytic water splitting reaction. The Pd/TiO₂ nanosheet catalysts showed immensely improved photocatalytic activities compared to pure TiO₂ nanosheets.

Hydrothermal synthesis of the novel rutile-mixed anatase TiO2 nanosheets with dominant {001} facets for high photocatalytic activity

We introduce a hydrothermal route to synthesize rutile-mixed anatase nanosheets with dominant {001} facets for high photocatalytic activity.

A novel approach to formulate high flux multifunctional ultrafiltration membranes from photocatalytic titania composite precursors on multi-channel tubular substrates

Anatase rich titanium dioxide ultrafiltration membranes with high filtration rates have been successfully developed on multi-channel tubular alumina substrates via aqueous sol–gel method from titania–alumina composite precursors.

The excellent photocatalytic synergism of PbBiO2Br/UiO-66-NH2 composites via multiple coupling effects

PbBiO₂Br/UiO-66-NH₂ composites synthesized by a facile solvothermal method have a core–shell structure with UiO-66-NH₂ forming the shell around a PbBiO₂Br core.

Fabrication of a novel ZnO/MMO/CNT nanohybrid derived from multi-cationic layered double hydroxide for photocatalytic degradation of azo dye under visible light

A facile and effective approach for assembling ZnO/MMO/CNT nanohybrid with excellent photodegradation performance under visible light is reported.

TiO2 Microwave Synthesis, Electrophoretic Deposition of Thin Film, and Photocatalytic Properties for Methylene Blue and Methyl Red Dyes

Electrophoretic deposition (EPD) of TiO2 thin film was carried out at room temperature on low cost steel substrate using microwave synthesized nanoparticles (NPs) of TiO2. Synthesized NPs and EPD thin film were characterized at different stages of synthesis for its crystal structure, morphology, elemental analysis, and surface area. Spherical particle morphology and formation of TiO2 were confirmed by scanning electron micrograph (SEM), energy dispersive spectrometer (EDS), and X-ray diffraction (XRD). Synthesized NPs were formed in anatase phase having crystallite size of about 12.3 nm from Scherrer's formula using full width half maxima (FWHM). Surface area was found to be 43.52 m2/g by BET giving particle size of 33 nm. Photocatalytic (PC) behavior of TiO2 NPs and EPD TiO2 film on steel substrate was investigated under UV light for two commercial dyes and their photocatalysis efficiency was analyzed. NPs have shown better efficiency for methylene blue (MB) dye than EPD film whereas EPD film have shown higher PC activity for methyl red (MR) dye.

Review on modified N–TiO2 for green energy applications under UV/visible light: selected results and reaction mechanisms

Modifications of the activity, band structure, morphology, optical and electronic properties of N–TiO₂ for energy and environmental applications.

A facile and efficient preparation of anatase titania nanoparticles in micelle nanoreactors: morphology, structure, and their high photocatalytic activity under UV light illumination

Comparative photocatalysis degradation of MB dye under ultraviolet light irradiation: (a) without photocatalyst; (b) commercial P25 TiO₂ powder; and (c) TiO₂ nanoparticles.

High efficiency photocatalytic conversion of CO2 with H2O over Pt/TiO2 nanoparticles

Pt/TiO₂ nanoparticles were prepared by a solvothermal method and used for high efficiency photocatalytic CO₂ conversion.