Synthesis of Pt-decorated CaTiO3 nanocrystals for efficient photoconversion of nitrobenzene to aniline under visible light

Photocatalytic Transformation of Organics to Valuable Chemicals - Quo Vadis?

Recent development in photocatalysis is increasingly focused on transforming organic compounds toward producing fine chemicals. Simple, non-selective oxidation reactions (degradation of pollutants) and very demanding solar-to-chemical energy conversion processes (production of solar fuels) face severe economic limitations influenced by still low efficiency and insufficient stability of the systems. Synthesis of fine chemicals, including reductive and oxidative selective transformations, as well as C-C and C-N coupling reactions, can utilise the power of photocatalysis. Herein, we present the recent progress in photocatalytic systems designed to synthesise fine chemicals. In particular, we discuss the factors influencing the efficiency and selectivity of the organic transformations, dividing them into intrinsic (related to individual properties of photocatalysts) and extrinsic (originating from the reaction environment). A rational design of the photocatalytic systems, based on a deep understanding of these factors, opens new perspectives for applied photocatalysis.

A Breakthrough in Photocatalytic Wastewater Treatment: The Incredible Potential of g-C3N4/Titanate Perovskite-Based Nanocomposites

Water pollution has emerged as a major global environmental crisis due to the massive contamination of water resources by the textile dyeing industry, organic waste, and agricultural residue. Since water is fundamental to life, this grave disregard puts lives at risk, making the protection of water resources a serious issue today. Recent research has shown great interest in improving the photocatalytic performance of graphitic carbon nitride (g-C3N4) for wastewater treatment. However, the photocatalytic removal activity of pure g-C3N4 is poor, owing to its minimal surface area, fast recombination of photo-generated electron-hole pairs, and poor light absorption. Recently, titanate perovskites (TNPs) have attracted significant attention in both environmental remediation and energy conversion due to their exceptional structural, optical, physiochemical, electrical, and thermal properties. Accordingly, TNPs can initiate a variety of surface catalytic reactions and are regarded as an emerging category of photocatalysts for sustainability and energy-related industries when exposed to illumination. Therefore, in this review article, we critically discuss the recent developments of extensively developed g-C3N4/TNPs that demonstrate photocatalytic applications for wastewater treatment. The different synthetic approaches and the chemical composition of g-C3N4/TNP composites are presented. Additionally, this review highlights the global research trends related to these materials. Furthermore, this review provides insight into the various photocatalytic mechanisms, including their potential impact and significance. Also, the challenges faced by such materials and their future scope are discussed.

The Photocatalytic Activity of CaTiO3 Derived from the Microwave-Melting Heating Process of Blast Furnace Slag

The extraction of titanium-bearing components in the form of CaTiO₃ is an efficient utilization of blast furnace slag. The photocatalytic performance of this obtained CaTiO₃ (MM-CaTiO₃) as a catalyst for methylene blue (MB) degradation was evaluated in this study. The analyses indicated that the MM-CaTiO₃ had a completed structure with a special length-diameter ratio. Furthermore, the oxygen vacancy was easier to generate on a MM-CaTiO₃(110) plane during the photocatalytic process, contributing to improving photocatalytic activity. Compared with traditional catalysts, MM-CaTiO₃ has a narrower optical band gap and visible-light responsive performance. The degradation experiments further confirmed that the photocatalytic degradation efficiency of pollutants by using MM-CaTiO₃ was 3.2 times that of pristine CaTiO₃ in optimized conditions. Combined with molecular simulation, the degradation mechanism clarified that acridine of MB molecular was stepwise destroyed by using MM-CaTiO₃ in short times, which is different from demethylation and methylenedioxy ring degradation by using TiO₂. This study provided a promising routine for using solid waste to obtain catalysts with excellent photocatalytic activity and was found to be in keeping with sustainable environmental development.

Visible-Light-Driven CO2 Reduction into Methanol Utilizing Sol-Gel-Prepared CeO2-Coupled Bi2O3 Nanocomposite Heterojunctions

Carbon dioxide (CO2) photoreduction into renewable fuels over semiconductor photocatalysts has emerged as a green and sustainable alternative for energy production. Consequently, tremendous efforts are being performed to develop robust and sustainable photocatalysts. Therefore, visible-light active nanocomposite photocatalysts composed of 5.0–20.0 wt.% bismuth oxide (Bi2O3) and cerium oxide (CeO2) were synthesized by a sol-gel-based process. The prepared nanocomposites were evaluated for the promoted photocatalytic reduction of CO2 into methanol (CH3OH). Various characterizations of the obtained photocatalysts exposed an outstanding development of crystalline structure, morphology, and surface texture due to the presence of Bi2O3. Moreover, the absorbance of light in the visible regime was improved with enhanced charge separation, as revealed by the exploration of optical response, photoluminescence, and photocurrent measurements. The overall bandgap calculations revealed a reduction to 2.75 eV for 15% Bi2O3/CeO2 compared to 2.93 eV for pure CeO2. Moreover, the adjusted 2.8 g L−1 dose of 15% Bi2O3/CeO2 selectively produced 1300 μmol g−1 CH3OH after 9 h of visible light irradiation. This photocatalyst also exhibits bearable reusability five times. The improved progression of 15% Bi2O3/CeO2 is denoted by significant charge separation as well as enhanced mobility. This study suggests the application of metal oxide-based heterojunctions for renewable fuel production under visible light.

CdO-supported ZrO2heterojunctions: facile synthesis and rapid visible-light oxidation of atrazine herbicide with superb recyclability

The advancement in ceramic oxide-based photocatalysis has got much attention recently for environmental issues. Atrazine (AZ) is one of the major used herbicides in agricultural and related industries. This work familiarizes a polymeric-assisted sol-gel preparation of high surface area zirconium oxide (ZrO₂) supported with cadmium oxide nanoparticles at minor content (0.5-2.0 wt%). Exploration of the synthesized heterostructures revealed the enhancement of visible-light absorbance and reduction of bandgap energy to 2.76 eV keeping the same crystalline form and high surface area of 170 m²g^‒1. The prepared photocatalysts were used to degrade AZ in water at a concentration of 231.8μM (50 ppm). The 1.5%-introduced CdO to ZrO₂revealed the best-performed photocatalyst for complete oxidation of AZ within 40 at an optimized dose of 1.6 g l^-1. This novel ceramic photocatalyst showed a chemical and structural ability to keep 98.5% of its initial efficiency after five regenerated cycles. The construction of p-n heterojunction between the p-type ZrO₂and the n-type CdO contributed to the comprehensive photocatalytic competence toward the efficient charge separation and photooxidation process.

Mesoporous BiVO4/TiO2 heterojunction: enhanced photoabsorption and photocatalytic ability through promoted charge transfer

BiVO₄ has been constructed into heterojunctions with TiO₂ to boost the photocatalytic ability under visible illumination. Here, mesoporous BiVO₄/TiO₂ nanocomposites have been fabricated by a facile sol-gel approach utilizing nonionic surfactant and addressed for morphological, optical, structural, and degradation of ciprofloxacin (CIP) in water under visible illumination as an antibiotic pollutant model. The TEM images demonstrated that the TiO₂ NPs are homogenous in terms of shape and size (15 ± 5 nm). The introduction of BiVO₄ into mesoporous TiO₂ could effectively enhance the rapid separation efficiency of the photoinduced carriers and optical absorption. The 3%BiVO₄/TiO₂ photocatalyst possessed the best degradation efficiency (100%) within 60 min which was promoted 20-folds larger than TiO₂ NPs (5%). 3%BiVO₄/TiO₂ nanocomposite exhibited the fastest degradation rate (2.15 × 10^-2 min^-1), which was 40 times faster than bare TiO₂ photocatalyst (0.05 × 10^-2 min^-1). The enhanced photocatalytic ability originated from superior charge separation characteristics and high solar energy absorption in mesopore structures. The recombination rate and mobility of charge carriers were characterized utilizing photoluminescence (PL) and photoelectrochemical measurements. This work highlights the advantages of mesoporous heterojunction BiVO₄/TiO₂ nanocomposites for photocatalytic performances and provides a multilateral route to design an effective wide-spectrum response photocatalyst for the development of comparable materials. The photocatalytic mechanism for degradation CIP over BiVO₄/TiO₂ was discussed in detail..

Visible-light photooxidation of ciprofloxacin utilizing metal oxide incorporated sol-gel processed La-doped NaTaO3 nanoparticles: A comparative study

The supper dissemination of antibiotic waste in water resources has exponentially progressed the vital water and soil pollution that affect human health and the environment. Consequently, there have been several types of research anticipated for the green mineralization of such pollutants. Herein, we intended a surfactant-aided sol-gel formation of lanthanum-doped sodium tantalate (LNTO) nanocrystals. The synthesized 13 nm averaged-size perovskite LNTO nanocrystals were responsive to visible-light irradiation by incorporation of 4.4-5.2 nm oxide nanoparticles, namely Bi₂O₃, CdO, Fe₂O₃, and CuO at 4.0 wt% through coprecipitation. The formed nanomaterials unveiled mesostructured surface textures with specific surface areas of 199-229 m² g^-1. The obtained nanoceramics were employed for the mineralization of 10 ppm of ciprofloxacin antibiotic (CPF) as an emerging antibiotic waste in water under visible light irradiation. The CuO-incorporated LNTO exhibited the best photocatalytic oxidation of CPF after 120 min compared with other oxides with an excellent photoreaction rate of 0.0343 min^-1 which is 49 times higher than the pure LNTO. The 2.0 gL^-1 CuO/LNTO-dose achieved the full photooxidation of CPF at an oxidation speed of 0.0738 min ^-1 within just 1.0 h of visible light irradiation and magnificent regeneration ability. This enhanced activity of CuO/LNTO is regarded as significant light absorption and a bandgap energy reduction to 2.12 eV. Besides that, the heterojunction between CuO and LNTO amended the photogenerated carrier mobility and separation as concluded from the photoluminescence and photocurrent exploration. This comparative work suggests the proper design of low bandgap oxide decoration of solution-based perovskite oxide photocatalysts for promoting the visible-light mineralization of antibiotics in water.

Photocatalytic Oxidative Desulfurization of Thiophene by Exploiting a Mesoporous V2O5-ZnO Nanocomposite as an Effective Photocatalyst

Due to increasingly stringent environmental regulations imposed by governments throughout the world, the manufacture of low-sulfur fuels has received considerable assiduity in the petroleum industry. In this investigation, mesoporous V2O5-decorated two-dimensional ZnO nanocrystals were manufactured using a simple surfactant-assisted sol–gel method for thiophene photocatalytic oxidative desulfurization (TPOD) at ambient temperature applying visible illumination. When correlated to pure ZnO NCs, V2O5-added ZnO nanocomposites dramatically improved the photocatalytic desulfurization of thiophene, and the reaction was shown to follow the pseudo-first-order model. The photocatalytic effectiveness of the 3.0 wt.% V2O5-ZnO photocatalyst was the greatest among all the other samples, with a rate constant of 0.0166 min−1, which was 30.7 significantly greater than that of pure ZnO NCs (0.00054 min−1). Compared with ZnO NCs, and owing to their synergetic effects, substantial creation of hydroxyl radical levels, lesser light scattering action, quick transport of thiophene species to the active recenters, and efficient visible-light gathering, V2O5-ZnO nanocomposites were found to have enhanced photocatalytic efficiency. V2O5-ZnO nanocomposites demonstrated outstanding stability during TPOD. Using mesoporous V2O5-ZnO nanocomposites, the mechanism of the charge separation process was postulated.

An emerging photocatalyst for wastewater remediation: a mini-review on CaCu3Ti4O12 photocatalysis

Ceramics-based filter for water treatment is an ancient technology to procure potable water at the household level. The traditional clay pots (vessels or hollow cylindrical container) have been used since long in the developing countries. The ceramic material (CaCu₃Ti₄O₁₂ or CCTO) is a hetero-junction of titanium oxide, a well-known UV-active photocatalyst, and visible light absorbing CuO materials. This hetero-junction is able to overcome the limitations such as high bandgap, poor stability, low efficiency, and high photo-generated charge (e^-/h⁺) recombination rate, associated with the other commonly used metal oxide semiconductor photocatalysts. Moreover, the low-cost, viable and facile synthesis routes for CCTO triggered its potential applications in photoelectrochemical and photocatalytic processes. This review will elaborate on the available literature demonstrating the visible light activity of CCTO photocatalysts in water treatment technologies. Furthermore, the mechanism of photocatalysis and synthesis routes are presented in this work for broader impact of the CCTO potential applications. The extended porous character and excellent surface texture have made the ceramic materials as an ideal choice to combat the bacteria, pathogens and turbidity in aqueous medium at household level. Specifically, the controlled size and shape make the CaCu₃Ti₄O₁₂ (CCTO) an excellent visible light-driven photocatalyst, involving highly reactive species such as ^•OH, ^•O₂^- anions, h⁺, and e^-, for the removal of organic and inorganic pollutants from water.

Synthesis and Photocatalytic Activity of Pt-Deposited TiO2 Nanotubes (TNT) for Rhodamine B Degradation

Dye wastewater has attracted more and more attention because of its high environmental risk. In this study, a novel TiO2 nanotube (TNT) catalyst was prepared and its morphology and structure were characterized. The synthetic catalyst was used to degrade Rhodamine B (RhB) under UV light and evaluated for the application performance. According to the characterization results and degradation properties, the optimum synthetic conditions were selected as 400°C calcination temperature and 10 wt% Pt deposition. As a result, the degradation efficacies were sequenced as TNT-400-Pt > TNT-500-Pt > TNT-400 > TNT-300-Pt. In addition, the effect of pH and initial concentration of RhB were explored, and their values were both increased with the decreased degradation efficacy. While the moderate volume of 11 mm of H2O2 addition owned better performance than that of 0, 6, and 15 mm. Scavengers such as tertbutanol (t-BuOH), disodium ethylenediaminetetraacetate (EDTA-Na2), and nitroblue tetrazolium (NBT) were added during the catalytic process and it proved that superoxide radical anions (O2–•), photogenerated hole (h+) and hydroxyl radical (OH•) were the main active species contributing for RhB removal. For the application, TNT-Pt could deal with almost 100% RhB, Orange G (OG), Methylene blue (MB), and Congo red (CR) within 70 min and still kept more than 50% RhB removal in the fifth recycling use. Therefore, TNT-Pt synthesized in this study is potential to be applied to the dye wastewater treatment.

Visible-light responsive ZnSe-anchored mesoporous TiO2heterostructures for boosted photocatalytic reduction of Cr(VI)

The accumulation of Cr(VI) ions in water can cause serious influences on the environment and human health. This work reports a humble synthesis of ZnSe nanoparticles anchored to the sol-gel prepared TiO₂for visible-light-driven photocatalytic reduction of Cr(VI) ions. The 7.9 nm ZnSe nanoparticles were attached to TiO₂surfaces at a content of 1.0-4.0 wt% as experiential by TEM investigation. The designed nanocomposite unveiled mesostructured surfaces exhibiting surface areas of 176-210 m²g^-1. The impregnation of ZnSe amended the visible-light absorption of TiO₂due to the bandgap decrease from 3.14 to 2.90 eV. The photocatalytic reduction of Cr(VI) applying the optimized portion of 3.0 wt% ZnSe/TiO₂was achieved at 177μmol min^-1. This photocatalytic activity is higher than the common Degussa P25 and pristine TiO₂by 20 and 30 times, respectively. The improved performance is signified by the efficient interfacial separation of charge carriers by the introduction of ZnSe. This innovative ZnSe/TiO₂has also shown photocatalytic stability for five consecutive runs.

XPS Study on Calcining Mixtures of Brucite with Titania

In this work, we studied the phases in a Mg-Ti-O system using a 1:1 formulation of MgO:TiO2, mixing synthetic brucite of Mexican origin with TiO2 microparticles of high purity, with a heat treatment at 1100 °C for 1 h. Due to its valence electrons, TiO2 can contribute to the sintering process to improve density in MgO products. The raw materials and formulation by XPS and X-RD techniques were characterized. The results demonstrate the presence of different oxidation states in titania and the formation of different oxides in the Mg-Ti-O system when mixed and calcined at 1100 °C; additionally, we estimated the formation of vacancies in the crystal lattice during the transformation from hexagonal brucite to magnesia with a cubic structure centered on the faces. Its thermal behavior is indicated by the MgO-TiO2 phase diagram.

CoAl2O4-g-C3N4 Nanocomposite Photocatalysts for Powerful Visible-Light-Driven Hydrogen Production

There is no doubt that the rate of hydrogen production via the water splitting reaction is profoundly affected to a remarkable degree based on the isolation of photogenerated electrons from holes. The precipitation of any cocatalysts on the substrate surfaces (including semiconductor materials) provides significant hindrance to such reincorporation. In this regard, a graphite-like structure in the form of mesoporous g-C₃N₄ formed in the presence of a template of mesoporous silica has been synthesized via the known combustion method. Hence, the resulting g-C₃N₄ nanosheets were decorated with varying amounts of mesoporous CoAl₂O₄ nanoparticles (1.0-4.0%). The efficiencies of the photocatalytic H₂ production by CoAl₂O₄-doped g-C₃N₄ nanocomposites were studied and compared with those of pure CoAl₂O₄ and g-C₃N₄. Visible light irradiation was carried out in the presence of glycerol as a scavenger. The results showed that the noticeable photocatalytic enhancement rate was due to the presence of CoAl₂O₄ nanoparticles distributed on the g-C₃N₄ surface. The 3.0% CoAl₂O₄-g-C₃N₄ nanocomposite had the optimum concentration. This photocatalyst showed extremely high photocatalytic activities that were up to 22 and 45 times greater than those of CoAl₂O₄ and g-C₃N₄, respectively. This photocatalyst also showed 5 times higher photocatalytic stability than that of CoAl₂O₄ or g-C₃N₄. The presence of CoAl₂O₄ nanoparticles as a cocatalyst increased both the efficiency and productivity of the CoAl₂O₄-g-C₃N₄ photocatalyst. This outcome was attributed to the mesostructures being efficient charge separation carriers with narrow band gaps and high surface areas, which were due to the presence of CoAl₂O₄.