Three-dimensional Fe2O3–TiO2–graphene aerogel nanocomposites with enhanced adsorption and visible light-driven photocatalytic performance in the removal of RhB dyes

Fe2O3/TiO2/reduced graphene oxide-driven recycled visible-photocatalytic Fenton reactions to mineralize organic pollutants in a wide pH range

Photocatalytic Fenton reactions combined the advantages from both photocatalysis and Fenton reaction in mineralizing organic pollutants. The key problems are the efficiency and recycling stability. Herein, we reported a novel Fe2O3/TiO2/reduced graphene oxide (FTG) nanocomposite synthesized by a facile solvothermal method. The TiO2 in FTG degraded organic pollutants and mineralized intermediates via photocatalysis under visible light irradiation, which could also promote Fenton reaction by accelerating Fe3+-Fe2+ recycle. Meanwhile, the Fe2O3 rapidly degraded organic pollutants via Fenton reactions, which also promoted photocatalysis by enhancing visible light absorbance and diminishing photoelectron-hole recombination. The high distribution of TiO2 and Fe2O3 on rGO, together with their strong interaction resulted in enhanced synergetic cooperation between photocatalysis and Fenton reactions, leading to the high mineralization efficiency of organic pollutants. More importantly, it could also inhibit the leaching of Fe species, leading to the long lifetime of FTG during photocatalytic Fenton reactions in a wide pH range from 3.4 to 9.2.

Metal ferrites-based nanocomposites and nanohybrids for photocatalytic water treatment and electrocatalytic water splitting

Photocatalytic degradation is one of the most promising technologies available for removing a variety of synthetic and organic pollutants from the environmental matrices because of its high catalytic activity, reduced energy consumption, and low total cost. Due to its acceptable bandgap, broad light-harvesting efficiency, significant renewability, and stability, Fe₂O₃ has emerged as a fascinating material for the degradation of organic contaminants as well as numerous dyes. This study thoroughly reviewed the efficiency of Fe₂O₃-based nanocomposite and nanomaterials for water remediation. Iron oxide structure and various synthetic methods are briefly discussed. Additionally, the electrocatalytic application of Fe₂O₃-based nanocomposites, including oxygen evolution reaction, oxygen reduction reaction, hydrogen evolution reaction, and overall water splitting efficiency, was also highlighted to illustrate the great promise of these composites. Finally, the ongoing issues and future prospects are directed to fully reveal the standards of Fe₂O₃-based catalysts. This review is intended to disseminate knowledge for further research on the possible applications of Fe₂O₃ as a photocatalyst and electrocatalyst.

Application of Synthesized Vanadium-Titanium Oxide Nanocomposite to Eliminate Rhodamine-B Dye from Aqueous Medium

In this study, a V@TiO₂ nanocomposite is examined for its ability to eliminate carcinogenic Rhodamine (Rh-B) dye from an aqueous medium. A simple ultrasonic method was used to produce the nanosorbent. In addition, V@TiO₂ was characterized using various techniques, including XRD, HRTEM, XPS, and FTIR. Batch mode studies were used to study the removal of Rh-B dye. In the presence of pH 9, the V@TiO₂ nanocomposite was able to remove Rh-B dye to its maximum extent. A correlation regression of 0.95 indicated that the Langmuir model was a better fit for dye adsorption. Moreover, the maximum adsorption capacity of the V@TiO₂ nanocomposite was determined to be 158.8 mg/g. According to the thermodynamic parameters, dye adsorption followed a pseudo-first-order model. Based on the results of the study, a V@TiO₂ nanocomposite can be reused for dye removal using ethanol.

Synthesis, Characterization, and Photocatalytic Activities of Graphene Oxide/metal Oxides Nanocomposites: A Review

Sustainable water processing techniques have been extensively investigated and are capable of improving water quality. Among the techniques, photocatalytic technology has shown great potential in recent years as a low cost, environmentally friendly and sustainable technology. However, the major challenge in the industrial development of photocatalyst technology is to develop an ideal photocatalyst which must have high photocatalytic activity, a large specific surface area, harvest sunlight and shows recyclability. Keeping these views, the present review highlighted the synthesis approaches of graphene/metal oxide nanocomposite, characterization techniques and their prominent applications in photocatalysis. Various parameters such as photocatalyst loading, structure of photocatalyst, temperature, pH, effect of oxidizing species and wavelength of light were addressed which could affect the rate of degradation. Moreover, the formation of intermediates during photo-oxidation of organic pollutants using these photocatalysts is also discussed. The analysis concluded with a synopsis of the importance of graphene-based materials in pollutant removal. Finally, a brief overview of the problems and future approaches in the field is also presented.

Fabrication of S-scheme CdS-g-C3N4-graphene aerogel heterojunction for enhanced visible light driven photocatalysis

Constructing S-scheme heterojunction photocatalysts reveals a greatly improved separation efficiency of photogenerated carriers and enhanced harvesting ability of solar energy in photocatalytic field. Herein, a ternary CdS-g-C₃N₄-GA heterojunction has been fabricated by a facile ultrasound strategy, which behaved as a S-scheme heterojunction with an intimate interface formed, and GA played as an electronic transportation platform to promote the separation of photo-induced charge carriers, which was certified through photoelectrochemical techniques. Density functional theory calculations revealed that the different component in ternary CdS-g-C₃N₄-GA heterojunction demonstrated an obvious difference of work function, resulting in the charge transfer from CdS to g-C₃N₄ through GA with S-scheme principle. In the optimized conditions, the S-scheme CdS-g-C₃N₄-GA heterojunction not only displayed greatly enhanced photocatalytic performances for degradation of dye and antibiotic wastewater, but also improved photocatalytic H₂ production activity. In addition, the photocatalytic mechanism and driving force of charge transfer and separation in S-scheme CdS-g-C₃N₄-GA heterojunction were studied. This study offers a feasible strategy to construct a ternary S-scheme heterojunction for environmental and energy photocatalysis.

One-Step Construction of Multi-Walled CNTs Loaded with Alpha-Fe2O3 Nanoparticles for Efficient Photocatalytic Properties

The aggregation and the rapid restructuring of the photoinduced electron−hole pairs restructuring in the process of photoelectric response remains a great challenge. In this study, a kind of Multi-walled carbon nanotubes loaded Alpha-Fe₂O₃ (CNTs/α-Fe₂O₃) heterostructure composite is successfully prepared via the one-step method. Due to the synergistic effect in the as-prepared CNTs/α-Fe₂O₃, the defect sites and oxygen-containing functional groups of CNTs can dramatically improve the interface charge separation efficiency and prevent the aggregation of α-Fe₂O₃. The improved photocurrent and enhanced hole–electron separation rate in the CNTs/α-Fe₂O₃ is obtained, and the narrower band gap is measured to be 2.8 ev with intensive visible-light absorption performance. Thus, the CNTs/α-Fe₂O₃ composite serves as an excellent visible light photocatalyst and exhibits an outstanding photocatalytic activity for the cationic dye degradation of rhodamine B (RhB). This research supplies a fresh application area forα-Fe₂O₃ photocatalyst and initiates a new approach for design of high efficiency photocatalytic materials.

Photocatalytic activity of G-TiO2@Fe3O4 with persulfate for degradation of alizarin red S under visible light

A composite photocatalyst combined with TiO₂, graphite (G) and Fe₃O₄ was prepared by co-precipitation method. Then the G-TiO₂@Fe₃O₄ was employed with persulfate (PS) to degrade alizarin red S (ARS) under visible light. The removal rate of ARS reached 100% after 60 min irradiation. The degradation rate constant of G-TiO₂@Fe₃O₄/PS exhibited 20.8, 9.0 and 3.1 times than that of TiO₂, G-TiO₂ and G-TiO₂@Fe₃O₄, respectively. The effects of photocatalyst dosage, mass ratios of graphite and Fe₃O₄ to TiO₂, PS dosage, initial pH and ARS concentration on the degradation efficiency were investigated. The optimal removal efficiency of ARS was obtained when G-TiO₂@Fe₃O₄ dosage was 0.25 g/L, G: TiO₂ = 0.005, Fe₃O₄: TiO₂ = 0.8, PS concentration was 6 mmol/L, initial pH = 3, and initial concentration of ARS was 100 mg/L. The SO₄·^- was demonstrated more important than O₂^- and·OH in the degradation of ARS. The intermediates and possible degradation pathways of ARS were discussed. Reuse and stability of G-TiO₂@Fe₃O₄ were also tested, and 88.3% photocatalytic activity was maintained after five cycles. Therefore, the proposed G-TiO₂@Fe₃O₄/PS not only had excellent photocatalytic activity, but also showed superior stability and reusability.

Graphene-based materials for adsorptive removal of pollutants from water and underlying interaction mechanism

Graphene-based materials have received much attention as attractive candidates for the adsorptive removal of pollutants from water due to their large surface area and diverse active sites for adsorption. The design of graphene-based adsorbents for target pollutants is based on the underlying adsorption mechanisms. Understanding the adsorption performance of graphene-based materials and its correlation to the interaction mechanisms between the pollutants and adsorbents is crucial to the further development of graphene-based functional materials and their practical applications. This review summarizes recent advances on the development of graphene-based materials for the adsorption of heavy metal ions, dyes, and oils, and the co-adsorption of their mixture from water. The material design, performance, regeneration and reuse of adsorbents, and the associated adsorption mechanisms are discussed. Various techniques for mechanistic studies of the adsorption of heavy metal ions, dyes, and oils on graphene-based materials are highlighted. The remaining challenges and perspectives for future development and investigation of graphene-based materials as adsorbents are also presented.

Recent Developments of TiO2-Based Photocatalysis in the Hydrogen Evolution and Photodegradation: A Review

The growth of industrialization, which is forced to use non-renewable energy sources, leads to an increase in environmental pollution. Therefore, it is necessary not only to reduce the use of fossil fuels to meet energy needs but also to replace it with cleaner fuels. Production of hydrogen by splitting water is considered one of the most promising ways to use solar energy. TiO₂ is an amphoteric oxide that occurs naturally in several modifications. This review summarizes recent advances of doped TiO₂-based photocatalysts used in hydrogen production and the degradation of organic pollutants in water. An intense scientific and practical interest in these processes is aroused by the fact that they aim to solve global problems of energy conservation and ecology.

A novel immobilized Z-scheme P3HT/α-Fe2O3 photocatalyst array: Study on the excellent photocatalytic performance and photocatalytic mechanism

The Z-scheme photocatalyst is valuable for use in polluted water purification. To improve the practical application value of the Z-scheme, in this study, a nano α-Fe₂O₃ and P3HT composite photocatalyst array was synthesized by electrophoretic deposition for the first time. This material was named F1P. The EPR, VBXPS and in situ illumination XPS analyses indicated that the charge transfer path of F1P conforms to the Z-scheme, and F1P array has a high light energy conversion efficiency. Due to the advantages of the Z-scheme system and the good light harvesting ability, F1P exhibited a good degradation effect on different types of pollutants under visible light irradiation. The degradation efficiency of tetracycline and bisphenol A by F1P can reach 97 % and 99 %, respectively. Moreover, F1P showed a certain resistance to water quality changes. After four cycles, F1P can maintain the structural stability and good pollutant treatment effect. Due to the high redox ability of F1P, the complex structure of pollutants can be destroyed and the degradation path of pollutants in F1P system was also analyzed. This study provides a new way of synthesizing Z-scheme systems and immobilizing Z-scheme photocatalysts. F1P is a new material with high practicability.

Reduced Graphene Oxide/ZIF-67 Aerogel Composite Material for Uranium Adsorption in Aqueous Solutions

Safe and sustainable development of the nuclear industry has become the focus of attention, so it is important to manage byproducts of radioactive elements, such as uranium, which is inevitably discharged into water bodies. In this work, an adsorbent was fabricated by the in-site assembly of zeolitic imidazolate framework-67 (ZIF-67) on reduced graphene oxide (rGO) hydrogel. The adsorption property of the rGO/ZIF-67 aerogel toward U(VI) was studied via batch adsorption experiment. According to kinetic fitting tests, the adsorption property was in accord well with the pseudo-second-order model, revealing that the adsorption process was chemisorption; the results of the isothermal model conform to the Langmuir model, which exhibited an excellent adsorption capacity of 1888.55 mg/g. The thermodynamic parameter (ΔH° = 11.7 kJ/mol) obtained from the experimental data demonstrated that temperature rise is favorable for the adsorption. Based on the characterization of the material and results of the adsorption, the adsorption mechanism for U(VI) may be explained by surface complexation and electrostatic attraction. In general, all these results and characteristics of the adsorbent show that the rGO/ZIF-67 aerogel provides an alternative way to fabricate novel uranium adsorbent.

A review on exploration of Fe2O3 photocatalyst towards degradation of dyes and organic contaminants

Photocatalytic degradation is among the promising technology for removal of various dyes and organic contaminants from environment owing to its excellent catalytic activity, low energy utilization, and low cost. As one of potential photocatalysts, Fe₂O₃ has emerged as an important material for degradation of numerous dyes and organic contaminants caused by its tolerable band gap, wide harvesting of visible light, good stability and recyclability. The present review thoroughly summarized the classification, synthesis route of Fe₂O₃ with different morphologies, and several modifications of Fe₂O₃ for improved photocatalytic performance. These include the incorporation with supporting materials, formation of heterojunction with other semiconductor photocatalysts, as well as the fabrication of Z-scheme. Explicitly, the other photocatalytic applications of Fe₂O₃, including for removal of heavy metals, reduction of CO₂, evolution of H₂, and N₂ fixation are also deliberately discussed to further highlight the huge potential of this catalyst. Moreover, the prospects and future challenges are also comprised to expose the unscrutinized criteria of Fe₂O₃ photocatalyst. This review aims to contribute a knowledge transfer for providing more information on the potential of Fe₂O₃ photocatalyst. In the meantime, it might give an idea for utilization of this photocatalyst in other environmental remediation application.

Improved in Situ Synthesis of Heterostructured 2D/2D BiOCl/g-C3N4 with Enhanced Dye Photodegradation under Visible-Light Illumination

A simple, in situ, and one-pot hydrothermal strategy was applied for the successful manufacturing of heterostructured 2D/2D BiOCl/g-C3N4 photocatalysts, and outstanding photodegradation of Rhodamine B in the condition of visible-light irradiation over the composites emerged. The investigation of various BiOCl/g-C3N4 ratios influencing the activity implied that the optimized B2C1 (mole ratio of BiOCl/g-C3N4 with 2:1) exhibited the higher degradation efficiency than that of the rest of the composites, even higher than that of pure BiOCl and pure g-C3N4, which yielded over 90% in the initial 30 min and reached almost 100% during the whole 70 min irradiation process. Kinds of characterizations demonstrated that the enhancement of photodegradation performance was caused by the intimate contact between BiOCl and g-C3N4 to form the heterostructure, which could benefit the generation of abundant visible-light photoinduced carriers and help enhance their separation and then promote their transportation to the surface.

Facile synthesis of GO and g-C3N4 nanosheets encapsulated magnetite ternary nanocomposite for superior photocatalytic degradation of phenol

In this study, the synthesis of Fe₃O₄@GO@g-C₃N₄ ternary nanocomposite for enhanced photocatalytic degradation of phenol has been investigated. The surface modification of Fe₃O₄ was performed through layer-by-layer electrostatic deposition meanwhile the heterojunction structure of ternary nanocomposite was obtained through sonicated assisted hydrothermal method. The photocatalysts were characterized for their crystallinity, surface morphology, chemical functionalities, and band gap energy. The Fe₃O₄@GO@g-C₃N₄ ternary nanocomposite achieved phenol degradation of ∼97%, which was significantly higher than that of Fe₃O₄@GO (∼75%) and Fe₃O₄ (∼62%). The enhanced photoactivity was due to the efficient charge carrier separation and desired band structure. The photocatalytic performance was further enhanced with the addition of hydrogen peroxide, in which phenol degradation up to 100% was achieved in 2 h irradiation time. The findings revealed that operating parameters have significant influences on the photocatalytic activities. It was found that lower phenol concentration promoted higher activity. In this study, 0.3 g of Fe₃O₄@GO@g-C₃N₄ was found to be the optimized photocatalyst for phenol degradation. At the optimized condition, the reaction rate constant was reported as 6.96 × 10^-3 min^-1. The ternary photocatalyst showed excellent recyclability in three consecutive cycles, which confirmed the stability of this ternary nanocomposite for degradation applications.

One-pot synthesis of 3D Cu2S–MoS2 nanocomposites by an ionic liquid-assisted strategy with high photocatalytic activity

Cu₂S–MoS₂ nanocomposites are synthesised by a one-step hydrothermal method and show better catalytic activity than Cu₂S and MoS₂ monomers.

Carbon/TiO2/Fe2O3 hybrid shells as efficient visible light photocatalysts

Mesoporous C/TiO₂/Fe₂O₃ hollow hybrids with TiO₂/Fe₂O₃ p–n heterojunctions and electrically conductive carbon show high photocatalytic performance.

Organic semiconductor/graphene oxide composites as a photo-anode for photo-electrochemical applications

An intimate physical mixture of graphene oxide (GO) and semiconducting organic molecules like bromophenathrene (BrPh) and bromopyrene (BrPy) was prepared by using a ball milling technique. The structural, microstructural, physical and chemical properties of the mixtures (20 wt% of GO) were analyzed by X-ray diffraction, SEM, FT-IR, TGA and TCSPC studies. Furthermore, the electrochemical properties like AC electrical conductivity, transient photocurrent response (PCTR) and open circuit voltage (OCVD) of the samples were analyzed. It has been observed from TCSPC and OCVD measurements that 20 wt% of GO in the semiconductor composite leads to an enhanced life-time of photo-generated charge carriers. The physical mixture composites exhibit a higher photocurrent than pure BrPh and BrPy.

New organic materials with longer life-times of the charge carrier and enhancement of photocurrent generation were developed.