Titanium dioxide and cadmium sulfide co-sensitized graphitic carbon nitride nanosheets composite photocatalysts with superior performance in phenol degradation under visible-light irradiation

Visible light driven (VLD) reduced TiO2-x nanocatalysts designed by inorganic and organic reducing agent-mediated solvothermal methods for electrocatalytic and photocatalytic applications

This work presents a comparative study on the structural, optical and electrochemical characteristics of visible light driven (VLD) reduced titanium dioxide (TiO2-x ) nanocatalysts synthesized via inorganic and organic synthetic routes. X-ray diffraction (XRD) patterns, Raman spectra and X-ray absorption fine structure (XAFS) analyses reflected anatase phase titania. Whereas, the quantitative EXAFS fit and XANES analysis revealed structural distortion due to the presence of oxygen and titanium vacancies with low valent Ti states in anatase lattices of certain nanocatalysts, which subsequently leads to better electrochemical and photocatalytic activities. Moreover, owing to the large surface area and mesoporous structures, the Mg-TiO2-x nanocatalysts exhibited enhanced water adsorption and ultimately increased overall water splitting with an OER overpotential equal to 420 mV vs. RHE at a current density of 10 mA cm-2 (Tafel slope = 62 mV dec-1), extended visible light absorbance, decreased photoluminescence (PL) intensity and increased carrier lifetime in comparison with commercial titania.

Nanofibers of chitosan-polycaprolactone blends as active support for photocatalytic nanoparticles: Outstanding role of chitosan in the degradation of an organic dye in water

Hybrid nanofibers of a chitosan-polycaprolactone blend containing titanium dioxide nanoparticles TiO2NPs, were prepared through electrospinning to study their adsorption and photocatalytic degradation capabilities of the model organic water pollutants, rhodamine B, RhB. To obtain uniform and bead-free nanofibers, an optimization of the electrospinning parameters was performed. The optimization was carried out by systematically adjusting the solution conditions (solvent, concentration, and polymer ratio) and instrumental parameters (voltage, needle tip-collector distance, and flow). The obtained materials were characterized by FT-IR, TGA, DSC, SEM, TEM, mechanical tensile test, and water contact angle. The photoactivity was investigated using a batch-type system by following UV-Vis absorbance and fluorescence of RhB. TiO2NPs were incorporated ex-situ into the polymer matrix, contributing to good mechanical properties and higher hydrophilicity of the material. The results showed that the presence of chitosan in the nanofibers significantly increased the adsorption of RhB and its photocatalytic degradation by TiO2NPs (5, 55 and 80 % of RhB degradation with NFs of PCL, TiO2/PCL and TiO2/CS-PCL, after 30 h of light irradiation, respectively), evidencing a synergistic effect between them. The results are attributed to an attraction of RhB by chitosan to the vicinity of TiO2NPs, favouring initial adsorption and degradation, phenomenon known as "bait-and-hook-and-destruct" effect.

Synthesis and application of titanium dioxide photocatalysis for energy, decontamination and viral disinfection: a review

Global pollution is calling for advanced methods to remove contaminants from water and wastewater, such as TiO₂-assisted photocatalysis.  The environmental applications of titanium dioxide have started after the initial TiO₂ application for water splitting by Fujishima and Honda in 1972. TiO₂ is now used for self-cleaning surfaces, air and water purification systems, microbial inactivation and selective organic conversion. The synthesis of titanium dioxide nanomaterials with high photocatalytic activity is actually a major challenge. Here we review titanium dioxide photocatalysis with focus on mechanims, synthesis, and applications. Synthetic methods include sol-gel, sonochemical, microwave, oxidation, deposition, hydro/solvothermal, and biological techniques. Applications comprise the production of energy, petroleum recovery, and the removal of microplastics, pharmaceuticals, metals, dyes, pesticides, and of viruses such as the severe acute respiratory syndrome coronavirus 2.

Non-Stacked γ-Fe2O3/C@TiO2 Double-Layer Hollow Nanoparticles for Enhanced Photocatalytic Applications under Visible Light

Herein, a non-stacked γ-Fe₂O₃/C@TiO₂ double-layer hollow nano photocatalyst has been developed with ultrathin nanosheets-assembled double shells for photodegradation phenol. High catalytic performance was found that the phenol could be completely degraded in 135 min under visible light, due to the moderate band edge position (VB at 0.59 eV and CB at −0.66 eV) of the non-stacked γ-Fe₂O₃/C@TiO₂, which can expand the excitation wavelength range into the visible light region and produce a high concentration of free radicals (such as ·OH, ·O²⁻, holes). Furthermore, the interior of the hollow composite γ-Fe₂O₃ is responsible for charge generation, and the carbon matrix facilitates charge transfer to the external TiO₂ shell. This overlap improved the selection/utilization efficiency, while the unique non-stacked double-layered structure inhibited initial charge recombination over the photocatalysts. This work provides new approaches for photocatalytic applications with γ-Fe₂O₃/C-based materials.

Photocatalytic Degradation of the Light Sensitive Organic Dyes: Methylene Blue and Rose Bengal by Using Urea Derived g-C3N4/ZnO Nanocomposites

In this study, we report the fabrication of graphitic carbon nitride doped zinc oxide nanocomposites, g-C3N4/ZnO, (Zn-Us) by using different amount of urea. They were further characterized by X-ray Diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), Raman, UV-vis, Scanning electron microscopy (SEM), and Transmission electron microscopy (TEM) techniques. The prepared nanocomposites were used as photocatalysts for the mineralization of the light sensitive dyes Methylene Blue (MB) and Rose Bengal (RB) under UV light irradiation, and corresponding photo-mechanism was proposed. Benefiting from these photocatalytic characteristics, urea derived g-C3N4/ZnO photocatalysts have been found to have excellent photodegradation activity against the MB and RB for 6 h and 4 h, respectively. Under the given experimental conditions, the degradation percentage of fabricated Zn-Us were shown ~90% for both model dyes. Compared to cationic MB dye, anionic RB dye is more actively degraded on the surface of prepared photocatalysts. The results obtained can be effectively used for future practical applications in wastewater treatment

Present applications of titanium dioxide for the photocatalytic removal of pollutants from water: A review

The evolution of modern technology and industrial processes has been accompanied by an increase in the utilization of chemicals to derive new products. Water bodies are frequently contaminated by the presence of conventional pollutants such as dyes and heavy metals, as well as microorganisms that are responsible for various diseases. A sharp rise has also been observed in the presence of new compounds heretofore excluded from the design and evaluation of wastewater treatment processes, categorized as "emerging pollutants". While some are harmless, certain emerging pollutants possess the ability to cause debilitating effects on a wide spectrum of living organisms. Photocatalytic degradation has emerged as an increasingly popular solution to the problem of water pollution due to its effectiveness and versatility. The primary objective of this study is to thoroughly scrutinize recent applications of titanium dioxide and its modified forms as photocatalytic materials in the removal and control of several classes of water pollutants as reported in literature. Different structural modifications are used to enhance the performance of the photocatalyst such as doping and formation of composites. The principles of these modifications have been scrutinized and evaluated in this review in order to present their advantages and drawbacks. The mechanisms involved in the removal of different pollutants through photocatalysis performed by TiO2 have been highlighted. The factors affecting the mechanism of photocatalysis and those affecting the performance of different TiO2-based photocatalysts have also been thoroughly discussed, thereby presenting a comprehensive view of all aspects involved in the application of TiO₂ to remediate and control water pollution.

Visible Light-Active CdS/TiO2 Hybrid Nanoparticles Immobilized on Polyacrylonitrile Membranes for the Photodegradation of Dyes in Water

Reusable photocatalytic polyacrylonitrile membrane-supported cadmium sulphide/titanium dioxide hybrid nanoparticles (CdS/TiO2-PAN) were prepared using a dry-wet phase inversion technique. Scanning electron microscopy (SEM) analysis revealed that the photocatalytic membranes had a porous sublayer, a compact top layer, and that, some of the nanoparticles were not encapsulated by the membranes. The average crystallite sizes of the CdS, TiO2, and CdS/TiO2 hybrid nanoparticles were 3.41 nm, 10.47 nm, and 12.17 nm, respectively. The combination of CdS and TiO2 nanoparticles led to a red shift (band gap; ca. 2.6 eV) of the absorption band and extended the optical absorption spectrum into the visible region relative to TiO2. The photocatalytic activity of CdS/TiO2-PAN membranes was explored in the degradation of methylene blue dye under visible light irradiation, and the results revealed that the best photocatalytic performance was achieved by 0.1 g CdS/TiO2-PAN photocatalytic membrane with 5% loading of the CdS/TiO2 hybrid nanoparticles, which degraded 66.29% of methylene blue in 210 minutes at 25°C and pH 8.5. It was found that the optimum loading of nanoparticles in the membranes was 0.1 g. All the photocatalytic membranes showed an insignificant decrease in the photocatalytic activity when used repeatedly. According to literature, CdS/TiO2-PAN photocatalytic membranes have not been prepared before for the purpose of treating simulated wastewater.

Toward an Accurate Spectrophotometric Evaluation of the Efficiencies of Photocatalysts in Processes Involving Their Separation Using Nylon Membranes

Many works include the use of nylon membranes to separate the solid particles of photocatalysts from the photocatalytic reactors, before using spectrophotometers to evaluate the catalysts’ performance in the photocatalytic degradation of many pollutants. This might lead to significant errors due to the adsorption of some pollutants within the structure of the membranes during the filtration process used to separate the solid particles of the photocatalysts to get a clear filtrate. This, consequently, leads to incorrect calculations, which in turn are translated into false high photocatalytic efficiencies of the used catalysts. In this work, the authors study the interaction between nylon membrane filters and five different model compounds—phenol red, methylene blue, rhodamine B, rhodamine 6G, and phenol. The study reveals a significant interaction between the nylon membranes and both rhodamine B and phenol red.

Effective Photocatalytic Hydrogen Evolution by Cascadal Carrier Transfer in the Reverse Direction

Visible-light-responsive photocatalysts used in the highly efficient hydrogen production exhibit several disadvantages such as photocorrosion and fast recombination. Because of the potential important applications of such catalysts, it is crucial that a simple, effective solution is developed. In this respect, in this study, we combined SiC (β modification) and TiO₂ with CdS to overcome the challenges of photocorrosion and fast recombination of CdS. Notably, we found that when irradiated with visible light, CdS was excited, and the excited electrons moved to the conduction band of TiO₂, thereby increasing the efficiency of charge separation. In addition, by moving the holes generated on CdS to the valence band of SiC, in the opposite direction of TiO₂, photocorrosion and fast recombination were prevented. As a result, in the sulfide solution, the CdS/SiC composite catalyst exhibited 4.3 times higher hydrogen generation ability than pure CdS. Moreover, this effect was enhanced with the addition of TiO₂, giving 10.8 times higher hydrogen generation ability for the CdS/SiC/TiO₂ catalyst. Notably, the most efficient catalyst, which was obtained by depositing Pt as a cocatalyst, exhibited 1.09 mmol g^-1 h^-1 hydrogen generation ability and an apparent quantum yield of 24.8%. Because water reduction proceeded on the TiO₂ surface and oxidative sulfide decomposition proceeded on the SiC surface, the exposure of CdS to the solution was unnecessary, and X-ray photoelectron spectroscopy confirmed that photocorrosion was successfully suppressed. Thus, we believe that the effective composite photocatalyst construction method presented herein can also be applied to other visible-light-responsive powder photocatalysts having the same disadvantages as CdS, thereby improving the efficiency of such catalysts.

Visible-light-driven activity and synergistic mechanism of TiO2@g-C3N4 heterostructured photocatalysts fabricated through a facile and green procedure for various toxic pollutants removal

Heterostructured photocatalysts based on g-C₃N₄ and TiO₂ represent a promising kind of photocatalyst in environmental fields, but the synthesis methods are always complex and not green. In the present paper, a facile and green one-step calcination procedure at lower temperature (450 °C) with the assistance of water is developed to synthesize a visible-light-active TiO₂@g-C₃N₄ heterostructured photocatalyst, which shows higher visible-light-driven activity (k = 0.014 min^-1) than pure g-C₃N₄ (k = 0.0036 min^-1) and TiO₂ (k = 0.0067 min^-1) for methyl orange degradation. Excellent performance (over 90% conversion) was also observed for the removal of rhodamine B, phenol, and Cr(VI) under visible light. The heterostructured photocatalyst showed favorable reusability, preserving 86% of its activity after five successive cycles. A mechanism study demonstrates that the enhanced photocatalytic activity results from the efficient separation of the photo-generated charge carriers through the intimate interface between the two semiconductors based on their appropriate band structures and light-induced mechanism. The heterostructured photocatalyst will certainly find wide applications in the treatment of various toxic pollutants in wastewater using abundant solar energy. Furthermore, this facile and green procedure and the proposed synergistic mechanism will provide guidelines in designing other g-C₃N₄ based organic-inorganic composite photocatalysts for various applications.

Visible Light-Controlled Inversion of Pickering Emulsions Stabilized by Functional Silica Microspheres

A new class of donor-acceptor Stenhouse adduct (DASA)-functionalized silica microspheres (SMs) is designed and described to formulate Pickering emulsions with inversion property and large polarity change upon visible light irradiation. By tuning the hydrophilicity of the functional SM particles with visible light, these Pickering emulsions can easily perform inversion from water-in-oil to oil-in-water. The inversion performance of the emulsions is ascribed to DASA photoisomerization from an extended, hydrophobic, and intensely purple-colored triene to a compact, zwitterionic, and colorless cyclopentenone upon irradiation with visible light. This unique inversion behavior has been applied to control encapsulation and the release of fluorescein sodium salt.

Tunable mechanisms of quantum efficiencies in CdSe and TiO2 quantum dot solar cells

The absorption spectra of CdSe/ZnO and TiO₂/MgZnO quantum dot (QD) solar cells were calculated, then their quantum efficiencies (QEs) were studied at different QD sizes and junction depths. Many mechanisms for tuning QE are examined. The first mechanism is doping the QD layer only, which is the case of CdSe, and it gives high QE. The second one is doping the bulk layer in addition to QDs, and it gives low QE but at a wide bandwidth, as in TiO₂/MgZnO QD solar cells. Changing QD size is also another mechanism that can tune QE and its spectrum. The structures studied cover the range of 120-370 nm, which is important in photodetecting applications.

Construction of a novel BiSI/MoS2 nanocomposite with enhanced visible-light driven photocatalytic performance

A BiSI/MoS₂ nanocomposite was synthesized for the first time and used as a new efficient and stable visible light driven photocatalyst.

An efficient eco advanced oxidation process for phenol mineralization using a 2D/3D nanocomposite photocatalyst and visible light irradiations

Nanocomposites (CNTi) with different mass ratios of carbon nitride (C₃N₄) and TiO₂ nanoparticles were prepared hydrothermally. Different characterization techniques were used including X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), transmission electron spectroscopy (TEM) and Brunauer-Emmett-Teller (BET). UV-Vis DRS demonstrated that the CNTi nanocomposites exhibited absorption in the visible light range. A sun light - simulated photoexcitation source was used to study the kinetics of phenol degradation and its intermediates in presence of the as-prepared nanocomposite photocatalysts. These results were compared with studies when TiO₂ nanoparticles were used in the presence and absence of H₂O₂ and/or O₃. The photodegradation of phenol was evaluated spectrophotometrically and using the total organic carbon (TOC) measurements. It was observed that the photocatalytic activity of the CNTi nanocomposites was significantly higher than that of TiO₂ nanoparticles. Additionally, spectrophotometry and TOC analyses confirmed that degraded phenol was completely mineralized to CO₂ and H₂O with the use of CNTi nanocomposites, which was not the case for TiO₂ where several intermediates were formed. Furthermore, when H₂O₂ and O₃ were simultaneously present, the 0.1% g-C₃N₄/TiO₂ nanocomposite showed the highest phenol degradation rate and the degradation percentage was greater than 91.4% within 30 min.

Two-dimensional carbon-based nanocomposites for photocatalytic energy generation and environmental remediation applications

In the pursuit towards the use of sunlight as a sustainable source for energy generation and environmental remediation, photocatalytic water splitting and photocatalytic pollutant degradation have recently gained significant importance. Research in this field is aimed at solving the global energy crisis and environmental issues in an ecologically-friendly way by using two of the most abundant natural resources, namely sunlight and water. Over the past few years, carbon-based nanocomposites, particularly graphene and graphitic carbon nitride, have attracted much attention as interesting materials in this field. Due to their unique chemical and physical properties, carbon-based nanocomposites have made a substantial contribution towards the generation of clean, renewable and viable forms of energy from light-based water splitting and pollutant removal. This review article provides a comprehensive overview of the recent research progress in the field of energy generation and environmental remediation using two-dimensional carbon-based nanocomposites. It begins with a brief introduction to the field, basic principles of photocatalytic water splitting for energy generation and environmental remediation, followed by the properties of carbon-based nanocomposites. Then, the development of various graphene-based nanocomposites for the above-mentioned applications is presented, wherein graphene plays different roles, including electron acceptor/transporter, cocatalyst, photocatalyst and photosensitizer. Subsequently, the development of different graphitic carbon nitride-based nanocomposites as photocatalysts for energy and environmental applications is discussed in detail. This review concludes by highlighting the advantages and challenges involved in the use of two-dimensional carbon-based nanocomposites for photocatalysis. Finally, the future perspectives of research in this field are also briefly mentioned.