ZnO nanowire arrays decorated 3D N-doped reduced graphene oxide nanotube framework for enhanced photocatalytic CO2 reduction performance

Recent Progress of Three-Dimensional Graphene-Based Composites for Photocatalysis

Converting solar energy into fuels/chemicals through photochemical approaches holds significant promise for addressing global energy demands. Currently, semiconductor photocatalysis combined with redox techniques has been intensively researched in pollutant degradation and secondary energy generation owing to its dual advantages of oxidizability and reducibility; however, challenges remain, particularly with improving conversion efficiency. Since graphene's initial introduction in 2004, three-dimensional (3D) graphene-based photocatalysts have garnered considerable attention due to their exceptional properties, such as their large specific surface area, abundant pore structure, diverse surface chemistry, adjustable band gap, and high electrical conductivity. Herein, this review provides an in-depth analysis of the commonly used photocatalysts based on 3D graphene, outlining their construction strategies and recent applications in photocatalytic degradation of organic pollutants, H2 evolution, and CO2 reduction. Additionally, the paper explores the multifaceted roles that 3D graphene plays in enhancing photocatalytic performance. By offering a comprehensive overview, we hope to highlight the potential of 3D graphene as an environmentally beneficial material and to inspire the development of more efficient, versatile graphene-based aerogel photocatalysts for future applications.

Photocatalytic CO2 Reduction to Ethanol by ZnCo2O4/ZnO Janus Hollow Nanofibers

Photocatalytic carbon dioxide (CO2) reduction for high-value hydrocarbon fuel production is a promising strategy to tackle global energy demand and climate change. However, this technology faces formidable challenges, primarily stemming from low yield and poor selectivity of C2 products of the desired hydrocarbon fuels. This study reported ZnO/ZnCo2O4 Janus hollow nanofibers (ZnO/ZCO JHNFs) prepared by electrospinning and atomic layer deposition. Photocatalytic tests revealed an ethanol yield of 4.99 μmol g-1 h-1 for ZnO/ZnCo2O4 JHNFs, surpassing mixed ZnO/ZnCo2O4 nanofibers (ZnO/ZCO NFs) by 4.35 times and pure ZnO by 12.7 times. The selectivity of 58.8% is 2.38 and 4.49 times higher than those of ZnO/ZnCo2O4 NFs and ZnO, respectively. These enhancements are attributed to efficient carrier separation facilitated by the ordered internal electric field of the Z-scheme heterojunction interface, validated by the energy band evaluations from experimentation and density functional theory (DFT) simulations and charge separation characterizations of photocurrent, impedance, and photoluminescence spectra. The Janus structure also effectively exposes the surface of ZnCo2O4 to CO2 molecules, increasing the active site availability, as confirmed by BET nitrogen adsorption/desorption, temperature-programmed desorption tests, and DFT adsorption energy calculations. This study proposes a novel approach for efficient photocatalytic hydrocarbon fuel production, with potential applications in energy and climate crisis mitigation.

Facile synthesis of MOF-808/RGO-based 3D macroscopic aerogel for enhanced photoreduction CO2

Three-dimensional (3D) macroscopic aerogels have emerged as a critical component in the realm of photocatalysis. Maximizing the integration of materials can result in enhanced efficiency and selectivity in photocatalytic processes. In this investigation, we fabricated MOF-808/reduced graphene oxide (RGO) 3D macroscopic aerogel composite materials employing the techniques of hydrothermal synthesis and freeze-drying. The results revealed that the macroscopic aerogel material exhibited the highest performance in CO2 reduction to CO, particularly when the concentration of RGO was maintained at 5 mg mL-1. In addition, we synthesized powder materials of MR-5 composite photocatalysts and conducted a comparative analysis in terms of photocatalytic CO2 reduction performance and electron transfer efficiency. The results showthat the macroscopic aerogel material boasts a high specific surface area, an abundant internal pore structure, and increased active sites. These attributes collectively enhance light energy utilization, and electron transfer rates, thereby, improving photothermal and photoelectric conversion efficiencies. Furthermore, we conducted in-situ FT-IR measurements and found that the M/R-5 aerogel exhibited the best CO2 adsorption capacity under a CO2 flow rate of 10 mL min-1. The density functional theory results demonstrate the correlation between the formation pathway of the product and the charge transfer pathway. This study provides useful ideas for realizing photocatalytic CO2 reduction of macroscopic aerogel materials in gas-solid reaction mode.

Spinach-derived boron-doped g-C3N4/TiO2 composites for efficient photo-degradation of methylene blue dye

Green synthesis of nanoparticles can be beneficial due to their low toxicity, cost-effectiveness, and environment-friendliness. Its synthesis involves the use of eco-friendly and biodegradable materials such as plant extracts, natural products, and microorganisms to reduce the negative environmental impacts of traditional nanoparticle synthesis methods. Herein, Spinacia oleracea leaves are used as a boron source, and a visible light active photo-catalyst is produced. The effect of Co-Catalyst Boron in Graphitic carbon nitride based nanocomposites for methylene blue dye photo-degradation in water is examined. Titanium dioxide (TiO₂) was activated by changing the hydrogen potential value while utilizing a typical orange dye as a sensitizer. The graphitic carbon nitride/TiO₂ nanocomposites were synthesized through a hydrothermal technique. To improve their performance, Boron used as a co-catalyst and B-doped g-C₃N₄/TiO₂nanocomposites prepared through wet chemical co-percipitate mathod. UV-visible spectroscopy, SEM and FTIR spectroscopy were used to analyze the photocatalyst and boron-doped composites in detail. The photocatalytic performance of pristine photocatalyst CNTx (x = 2%,4%,6%,8%) and B-doped CNTx composites were examined for Methylene Blue degradation in the presence of a light source. The spectroscopy analysis showed that B-doped g-C₃N₄/TiO₂ -8% nano-composites performed better than all other synthesized pristine catalysts and composites in this research. This research has demonstrated that B-doped g-C₃N₄/TiO₂ composites can provide an ideal solution for treating polluted water using visible light as a source to activate these photocatalysts.

An Update on Graphene Oxide: Applications and Toxicity

Graphene oxide (GO) has attracted much attention in the past few years because of its interesting and promising electrical, thermal, mechanical, and structural properties. These properties can be altered, as GO can be readily functionalized. Brodie synthesized the GO in 1859 by reacting graphite with KClO3 in the presence of fuming HNO3; the reaction took 3-4 days to complete at 333 K. Since then, various schemes have been developed to reduce the reaction time, increase the yield, and minimize the release of toxic byproducts (NO2 and N2O4). The modified Hummers method has been widely accepted to produce GO in bulk. Due to its versatile characteristics, GO has a wide range of applications in different fields like tissue engineering, photocatalysis, catalysis, and biomedical applications. Its porous structure is considered appropriate for tissue and organ regeneration. Various branches of tissue engineering are being extensively explored, such as bone, neural, dentistry, cartilage, and skin tissue engineering. The band gap of GO can be easily tuned, and therefore it has a wide range of photocatalytic applications as well: the degradation of organic contaminants, hydrogen generation, and CO2 reduction, etc. GO could be a potential nanocarrier in drug delivery systems, gene delivery, biological sensing, and antibacterial nanocomposites due to its large surface area and high density, as it is highly functionalized with oxygen-containing functional groups. GO or its composites are found to be toxic to various biological species and as also discussed in this review. It has been observed that superoxide dismutase (SOD) and reactive oxygen species (ROS) levels gradually increase over a period after GO is introduced in the biological systems. Hence, GO at specific concentrations is toxic for various species like earthworms, Chironomus riparius, Zebrafish, etc.

Visible-light-driven photocatalytic N2 fixation to nitrates by 2D/2D ultrathin BiVO4 nanosheet/rGO nanocomposites

Photocatalytic nitrogen fixation is a promising approach owing to its environmental friendliness and cost-effectiveness. The 2D/2D BiVO₄/rGO hybrid developed in this study exhibits a high nitrate-production rate of 1.45 mg h^-1 g^-1 and an apparent quantum efficiency (QE) of 0.64% at 420 nm, which represents one of the most highly active photocatalysts reported thus far.