Preparation of flower-like TiO2 sphere/reduced graphene oxide composites for photocatalytic degradation of organic pollutants

A Targeted Review of Current Progress, Challenges and Future Perspective of g-C3 N4 based Hybrid Photocatalyst Toward Multidimensional Applications

The increasing demand for searching highly efficient and robust technologies in the context of sustainable energy production totally rely onto the cost-effective energy efficient production technologies. Solar power technology in this regard will perceived to be extensively employed in a variety of ways in the future ahead, in terms of the combustion of petroleum-based pollutants, CO₂ reduction, heterogeneous photocatalysis, as well as the formation of unlimited and sustainable hydrogen gas production. Semiconductor-based photocatalysis is regarded as potentially sustainable solution in this context. g-C₃ N₄ is classified as non-metallic semiconductor to overcome this energy demand and enviromental challenges, because of its superior electronic configuration, which has a median band energy of around 2.7 eV, strong photocatalytic stability, and higher light performance. The photocatalytic performance of g-C₃ N₄ is perceived to be inadequate, owing to its small surface area along with high rate of charge recombination. However, various synthetic strategies were applied in order to incorporate g-C₃ N₄ with different guest materials to increase photocatalytic performance. After these fabrication approaches, the photocatalytic activity was enhanced owing to generation of photoinduced electrons and holes, by improving light absorption ability, and boosting surface area, which provides more space for photocatalytic reaction. In this review, various metals, non-metals, metals oxide, sulfides, and ferrites have been integrated with g-C₃ N₄ to form mono, bimetallic, heterojunction, Z-scheme, and S-scheme-based materials for boosting performance. Also, different varieties of g-C₃ N₄ were utilized for different aspects of photocatalytic application i. e., water reduction, water oxidation, CO₂ reduction, and photodegradation of dye pollutants, etc. As a consequence, we have assembled a summary of the latest g-C₃ N₄ based materials, their uses in solar energy adaption, and proper management of the environment. This research will further well explain the detail of the mechanism of all these photocatalytic processes for the next steps, as well as the age number of new insights in order to overcome the current challenges.

Synthesis and enhanced photocatalytic application of porous nanocomposites of (r)GO/TiO2 embedded HCP (hyper crosslinked polymer)

Nanocomposites (r)GO/TiO₂/hyper crosslinked polymer (HCP) were prepared using ultrasonic-assisted method, and identified by (SEM), (EDS), (TEM), and (XRD) techniques. This study was performed to examine the effect of various operating parameters on photocatalytic degradation of Rhodamine B (Rh.B) over (r)GO/TiO₂ embedded HCP followed by an optimization study using response surface methodology (RSM) based on Box-Behnken design (BBD). The photocatalytic activity of rGO/TiO₂/polycalix[4]resorcinarene ((r)GTP) was evaluated using the cationic dye Rhodamine B as a pollutant model under solar light (intensity = 850 W/m²) between 10 and 12 am, June, Ahvaz, Iran. Response Surface Methodology was adopted for the optimization of degradation parameters viz pH, dye concentration, and nanocomposites dosage and contact time. The optimum values for the maximum Rhodamine B (Rh B) degradation of rGO/TiO₂/polycalix (rGTP) and GTP were obtained, in which the degradation of rGTP was 100% and the degradation efficiency of GO/TiO₂/polycalix (GTP) was 70%. ANOVA analysis results demonstrated that irradiation time and nanocomposite mass were the most significant parameters. It was found that rGO/TiO₂/polycalix[4]resorcinarene (rGTP) nanocomposite displayed the best degradation yield for the dye. The results showed that the rGTP nanocomposite displayed good EIS and CV properties besides being eco-friendly and reusable. It could also show a high capacity for the elimination of the dye in the industrial wastewaters.

Graphene-based TiO2 composites for photocatalysis & environmental remediation: synthesis and progress

Photoactive nanomaterials constitute an emerging field in nanotechnology, finding an extensive array of applications spanning diverse areas, including electronics and photovoltaic devices, solar fuel cells, wastewater treatment, etc. Titanium dioxide (TiO₂), in its thin-film form, has been exhaustively surveyed as potential photocatalysts for environmental remediation owing to its innocuousness, stability, and photocatalytic characteristics when subjected to ultraviolet (UV) irradiation. However, TiO₂ has some shortcomings associated with a large bandgap value of around 3.2 eV, making it less efficient in the visible spectral range. TiO₂ is often consolidated with various carbon nanomaterials to overcome this limitation and enhance its efficiency. Graphene, a 2-dimensional allotrope of carbon with a bandgap tuned between 0 and 0.25 eV, exhibits unique properties, making it an attractive candidate to augment the photoactivity of semiconductor (SC) oxides. Encapsulating graphene oxide onto TiO₂ nanospheres demonstrates intensified photocatalytic properties and exceptional recyclability for the degeneration of certain dyes, including Rhodamine B. This review encompasses various techniques to synthesize graphene-based TiO₂ photoactive composites, emphasizing graphene capsulized hollow titania nanospheres, nanofibers, core/shell, and reduced graphene oxide-TiO₂-based nanocomposites. It also consolidates the application of the aforestated nanocomposites for the disintegration of various synthetic dyes, proving efficacious for water decontamination and degradation of chemicals and pharmaceuticals. Furthermore, graphene-based TiO₂ nanocomposites used as lithium (Li)-ion batteries manifesting substantial electrochemical performance and solar fuel cells for energy production are discussed here.

Impact of Doping and Additive Applications on Photocatalyst Textural Properties in Removing Organic Pollutants: A Review

The effect of ion doping and the incorporation of additives on photocatalysts’ textural properties have been reviewed. Generally, it can be summarised that ion doping and additives have beneficial effects on photocatalytic efficiency and not all have an increase in the surface area. The excessive amount of dopants and additives will produce larger aggregated particles and also cover the mesoporous structures, thereby increasing the pore size (Pd) and pore volume (Pv). An excessive amount of dopants also leads to visible light shielding effects, thus influence photocatalytic performance. Ion doping also shows some increment in the surface areas, but it has been identified that synergistic effects of the surface area, porosity, and dopant amount contribute to the photocatalytic performance. It is therefore important to understand the effect of doping and the application of additives on the textural properties of photocatalysts, thus, their performance. This review will provide an insight into the development of photocatalyst with better performance for wastewater treatment applications.

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.

Graphitic Carbon Nitride Materials for Photocatalytic Hydrogen Production via Water Splitting: A Short Review

The generation of photocatalytic hydrogen via water splitting under light irradiation is attracting much attention as an alternative to solve such problems as global warming and to increase interest in clean energy. However, due to the low efficiency and selectivity of photocatalytic hydrogen production under solar energy, a major challenge persists to improve the performance of photocatalytic hydrogen production through water splitting. In recent years, graphitic carbon nitride (g-C3N4), a non-metal photocatalyst, has emerged as an attractive material for photocatalytic hydrogen production. However, the fast recombination of photoexcited electron–hole pairs limits the rate of hydrogen evolution and various methods such as modification, heterojunctions with semiconductors, and metal and non-metal doping have been applied to solve this problem. In this review, we cover the rational design of g-C3N4-based photocatalysts achieved using methods such as modification, metal and non-metal doping, and heterojunctions, and we summarize recent achievements in their application as hydrogen production photocatalysts. In addition, future research and prospects of hydrogen-producing photocatalysts are also reviewed.

Recent Advances in Carbonaceous Photocatalysts with Enhanced Photocatalytic Performances: A Mini Review

Photocatalytic processes based on various semiconductors have been widely utilized in different applications, with great potential for use in environmental pollution remediation and sustainable energy generation. However, critical issues, including low light adsorption capability, wide energy bandgap, and unsatisfactory physicochemical stability still seriously limit the practical applications of photocatalysts. As a solution, the introduction of carbonaceous materials with different structures and properties into a photocatalyst system to further increase the activity has attracted much research attention. This mini review surveys the related literatures and highlights recent progress in the development of carbonaceous photocatalysts, which include various metal semiconductors with activated carbon, carbon dots, carbon nanotubes/nanofibers, graphene, fullerene, and carbon sponges/aerogels. Moreover, graphitic carbon nitride is also discussed as a carbon-rich and metal-free photocatalyst. The recently developed synthesis strategies and proposed mechanisms underlying the photocatalytic activity enhancement for different applications are summarized and discussed. Finally, ongoing challenges and the developmental direction for carbonaceous photocatalysts are proposed.

Controlled synthesis of Bi2O3/TiO2 catalysts with mixed alcohols for the photocatalytic oxidation of HCHO

Bi₂O₃/TiO₂ photocatalysts were prepared by a hydrothermal method. The photocatalysts were applied to the catalytic oxidation of indoor formaldehyde vapors under irradiation by an light-emitting diode energy-saving lamp. The characterization methods including Brunauer-Emmett-Teller, X-ay diffraction, UV-vis spectra, scanning electron microscopy, Transmission electron microscopy and X-ray photoelectron spectroscopy analysis were used to investigate the crystalline structure, morphology, specific surface area and porosity. The effects of the preparation conditions, including the type of alcohols, molar ratio and calcination temperature, on the morphology, structure and crystalline phase of the catalyst were also investigated. The results reveal that the morphology could be controlled by using different types of alcohols, especially mixed alcohols. The morphology played a key role in determining the photodegradation efficiency of formaldehyde. According to the experimental results, the Bi₂O₃/TiO₂ catalysts with amorphous particles showed the highest activity. The presence of anatase TiO₂ and Bi₄(TiO₄)₃ with a heterojunction structure was the main reason for the high activity, and they were beneficial for increasing the separation of the photogenerated electrons and holes and decreasing their recombination through electron transformations.

Titanium Dioxide/Graphene and Titanium Dioxide/Graphene Oxide Nanocomposites: Synthesis, Characterization and Photocatalytic Applications for Water Decontamination

The use of titanium dioxide, TiO2 as a photocatalyst in water decontamination has witnessed continuous interest due to its efficiency, stability, low toxicity and cost-effectiveness. TiO2 use is limited by its large band gap energy leading to light absorbance in the UV region of the spectrum, and by the relatively fast rate of recombination of photogenerated electrons and positive holes. Both limitations can be mitigated by using carbon-TiO2 nanocomposites, such as those based on graphene (G) and graphene oxide (GO). Relative to bare TiO2, these nanocomposites have improved photocatalytic activity and stability under the UV–visible light, constituting a promising way forward for improved TiO2 photocatalytic performance. This review focuses on the recent developments in the chemistry of TiO2/G and TiO2/GO nanocomposites. It addresses the mechanistic fundamentals, briefly, of TiO2 and TiO2/G and TiO2/GO photocatalysts, the various synthesis strategies for preparing TiO2/G and TiO2/GO nanocomposites, and the different characterization techniques used to study TiO2/G and TiO2/GO nanocomposites. Some applications of the use of TiO2/G and TiO2/GO nanocomposites in water decontamination are included.

Synthesis, Characterization, and Photocatalytic Properties of Bamboo Charcoal/TiO₂ Composites Using Four Sizes Powder

Visible-light-active bamboo biochar/TiO₂ composites were fabricated by the calcination method using C₁₆H₃₆O₄Ti as the titanium source and bamboo powder with different sizes as the carbon source. The TiO₂ nanoparticles were observed to disperse onto the surface of bamboo biochar fiber. The sizes of the bamboo powder played an important role in the microstructures and the properties of bamboo biochar/TiO₂ composites. The bamboo biochar/TiO₂ composites displayed the photocatalytic activities both under visible light irradiation and UV irradiation. The adsorption isotherms better fitted Freundlich isotherm models and the photodegradation reactions followed pseudo-first-order kinetics. Bamboo charcoal/TiO₂ composites exhibited high stability after up to four cycles. This research could pave the way for high-value applications of biomass in the environmental field.

A novel 3D heteropoly blue type photo-Fenton-like catalyst and its ability to remove dye pollution

A environment-friendly 3D inorganic heteropoly blue (HPB) Ba₂Na₂ [HPW^V₄W^VI₈O₄₀]·26H₂O was directly synthesized by hydrothermal method and characterized by means of ICP, IR, XPS, X-ray single crystal and X-ray powder diffraction. It was an efficient heterogeneous photo-Fenton-like catalyst to degrade anionic dye methyl orange under visible light irradiation. It removed cationic dyes methylene blue in neutral environment and rhodamine B in acidic condition via flocculation. The removal efficiency of methylene blue and rhodamine B by flocculation was more than 95%. Moreover, it could degrade methyl orange and flocculate rhodamine B at the same time. For MO and MO-RhB solutions, the degradation rates of MO in 60 min were 85.5% and 49.1%, respectively. Furthermore, the possible pathways for the production of active species in the MO degradation reaction were discussed. This is the first HPB constructed with 4e-reduced phosphotungstate, Ba and Na ions, having the properties of photo-Fenton-like catalyst and flocculant.