A comparative study of reduced graphene oxide modified TiO2, ZnO and Ta2O5 in visible light photocatalytic/photochemical oxidation of methylene blue

Reduced graphene oxide (rGO) was applied to prepare various composites of rGO/photocatalyst of G/TiO2, G/ZnO and G/Ta2O5, using titanium (IV) isopropoxide, Zn powder and commercial Ta2O5 powder as photocatalyst precursors, respectively. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric-differential thermal analysis (TG-DTA) and UV–vis diffuse reflectance (UV–vis DRS) were employed to investigate the crystal structure, morphology, surface groups, rGO loading, and optical properties of the produced composites. The photocatalytic activities of the composites under UV–vis and visible light were studied in degradation of methylene blue (MB). G/Ta2O5 showed an enhanced efficiency under UV–vis irradiation. G/TiO2 demonstrated an effective degradation of MB under visible light. The effects of various oxidants, peroxymonosulfate (PMS), peroxydisulfate (PDS) and hydrogen peroxide (H2O2) on MB degradation were thoroughly investigated. H2O2 was a promising oxidant for promoting MB degradation under visible light. The mechanism of the enhanced efficiency in the system of G/TiO2+ vis + H2O2 was discussed

Rational catalyst design for N2 reduction under ambient conditions: Strategies towards enhanced conversion efficiency

Ammonia (NH3), one of the basic chemicals in most fertilizers and a promising carbon-free energy storage carrier, is typically synthesized via the Haber–Bosch process with high energy consumption and massive emission of greenhouse gases. The photo/electrocatalytic nitrogen reduction reaction (NRR) under ambient conditions has attracted increasing interests recently, providing alternative routes to realize green NH3 synthesis. Despite rapid advances achieved in this most attractive research field, the unsatisfactory conversion efficiency including a low NH3 yield rate, and limited Faradaic efficiency or apparent quantum efficiency still remains as a great challenge. The NRR performance is intrinsically related to the electronic and surface structure of catalysts. Rational design and preparation of advanced catalysts are indispensable to improve the performance (e.g., activity and selectivity) of NRR. In this Review, various strategies for the development of desirable catalysts are comprehensively summarized, mainly containing the defect engineering, structural manipulation, crystallographic tailoring, and interface regulation. State-of-the-art heterogeneous NRR catalysts, prevailing theories and underlying catalytic mechanisms, together with current issues, critical challenges, and perspectives are discussed. It is highly expected that this Review will promote the understanding of recent advances in this area and stimulate greater interests for designing promising NRR catalysts in future

Effects of nitrogen-, boron-, and phosphorus-doping or codoping on metal-free graphene catalysis

Graphene-based materials have been demonstrated as excellent alternatives to traditional metal-based catalysts in environmental remediation. The metal-free nature of the nanocarbons can completely prevent toxic metal leaching and the associated secondary contamination. In this study, nitrogen doped graphene (NG) at a doping level of 6.54 at.% was prepared at mild conditions. Moreover, B- and P-doping or codoping with N in graphene were also achieved by a simple route. The modified graphene can efficiently activate peroxymonosulfate (PMS) to produce sulfate radicals to oxidize phenol solutions. Kinetic studies indicated that initial phenol concentration, PMS dosage, and temperature presented significant influences on the degradation rates. Electron paramagnetic resonance (EPR) analysis provided further insights into the evolution of active radicals during the activation of PMS and SO4•− was believed to be the primary radicals in the oxidation reactions. This study demonstrated a metal-free material for green catalysis in environmental remediation

Activated carbons as green and effective catalysts for generation of reactive radicals in degradation of aqueous phenol

Several activated carbons (ACs) were used as metal-free catalysts for degradation of a toxic organiccompound, phenol, in the presence of different oxidants, H2O2, peroxydisulfate (PS) and peroxymonosulfate (PMS). It was found that ACs were effective in heterogeneous activation of PMS toproduce sulfate radicals for degradation of phenol, much better than H2O2 and PS. Particle size of AC significantly influenced AC activity, and powder AC was much more effective than granular AC. The complete phenol removal could be achieved in 15 min on powder activated carbon (PAC) under the conditions of [phenol] = 25 mg L-1, [PAC] = 0.2 g L-1, [PMS] = 6.5 mmol L-1, and T = 25 degrees Celcius. It was also found that phenol degradation was significantly influenced by PMS loading, catalyst loading, phenol concentration and temperature. Surface activation of PMS and phenol adsorption played important roles in phenol degradation. Surface coverage by intermediate adsorption and structural change induced deactivation of AC and catalytic activity could be partially recovered by regeneration using calcination

Co3O4 nanocrystals with predominantly exposed facets: Synthesis, environmental and energy applications

Facet-dependent properties of novel metal or metal-oxide nanocrystals were discovered recently, and are attracting intensive interest owing to their great potential for various practical applications. Co3O4 as an important transition metal oxide shows electronic, magnetic, and redox properties which have found many applications in energy conversion and storage, magnetic separation, sensor devices and catalysis. This review summarizes the most recent research advances in synthesis and applications of nanosized Co3O4 with predominantly exposed facets, with emphasis on the enhanced performances in catalysis and electrochemical properties. The mechanism for improved selectivity and activity was discussed, and a panorama of the correlations between particle shape, crystal plane, surface atom arrangement, and active sites has been drawn. Insightful findings in this scope may be achieved by forthcoming research in theoretical calculations, rational synthesis, and emerging applications. Thus, researchers can manipulate the synthesis at the atomic level resulting in novel applications of the materials in a wide variety of areas

One-pot hydrothermal synthesis of Co(OH)2 nanoflakes on graphene sheets and their fast catalytic oxidation of phenol in liquid phase

A cobalt hydroxide (Co(OH)2) nanoflake-reduced graphene oxide (rGO) hybrid was synthesized by a onepot hydrothermal method using glucose as a reducing agent for graphene oxide (GO) reduction. The structural and surface properties of the material were investigated by scanning and transmission electron microscopies, energy-dispersive X-ray spectrometry, powder X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis. Catalytic activities of GO, rGO, Co(OH)2 and Co(OH)2–rGOin aqueous phenol degradation using peroxymonosulfate as an oxidant were compared. A synergetic effect on the catalytic activity was found on the Co(OH)2–rGO hybrid. Although rGO has weak catalytic activity, Co(OH)2–rGO hybrid showed a higher catalytic activity than Co(OH)2. The phenol degradation on Co(OH)2–rGO was extremely fast and took around 10 min for 100% phenol removal. The degradation was found to follow the first order kinetics and a mechanism for phenol degradation was presented

Pt-Free microengines at extremely low peroxide levels

Herein, we demonstrate that iron oxide modified MnO2 (FeOx-MnO2) catalyzed micromotors can be fabricated via electrochemical co-reduction and exhibit exceptional high performance at an extremely low hydrogen peroxide (H2O2) fuel concentration. We observed that graphene/FeOx-MnO2 microtubes could show motion behaviors at fuel concentration as low as 0.03% H2O2, which is nearly one order of magnitude lower than Pt-based micromotors (normally at above 0.2% H2O2). Moreover, the micromotors exhibit higher speeds than any other reported catalytic micro/nanomotors (MNMs) at low peroxide levels. The FeOx-MnO2 systems are better catalytic MNMs, due to their excellent catalytic activity, easy fabrication, robust structure and movement, as well as low-cost, biocompatible and abundance nature, showing great potential for future applications

Photothermal catalysis: From fundamentals to practical applications

Photothermal catalysis is an innovative approach that integrates photochemical and thermocatalytic processes to enable an efficient use of full-spectrum sunlight in catalyzing various chemical reactions for energy conversion and environmental governance. This approach has demonstrated competitive performance and energy efficiency compared to conventional techniques, making it suitable for large-scale applications. In this review, we will comprehensively examine the fundamentals and classification of photothermal catalysis and discuss detailed design principles of various types of photothermal catalysts, focusing on enhancing solar light absorption, improving internal electric field for more energetic hot carriers (EHC) and localized thermal energy (LTE), interfacial engineering for robust and directed EHC transferring, and regulating EHC and LTE for continuous 24/7 operation. We will also report photothermal catalysis in a diverse range of chemical reactions. Moreover, we will introduce the latest technologies for synthesizing robust photothermal catalysts and advanced solar concentrators for pilot testing in the production of solar fuels at scale. Finally, the future opportunities and challenges of the promising but fledging field will be discussed, which is expected to transform conventional chemical industries into a clean and sustainable manner

Corrosion behavior and mechanisms of the heat-treated Ti5Cu produced by laser powder bed fusion

This work investigated the corrosion behavior of laser powder bed fusion produced (LPBFed) Ti5Cu and its heat-treated counterparts at 740 and 900 °C (named as HT-740 and HT-900 respectively) in Hank’s solution. The results indicated that the presence of acicular a\u27-Ti phase in LPBFed Ti5Cu was beneficial to corrosion, but the corrosion resistance of HT-740 and HT-900 were increased owing to the dual-phase microstructure (a\u27/a-Ti + Ti2Cu) or the increased content of Ti2Cu phase in the microstructure. The Ti2Cu phase could provide an ‘envelope’ protection to the a\u27/a-Ti phase and slow down the micro-galvanic reaction between a\u27/a-Ti phase and Ti2Cu phase

Synthesis of porous reduced graphene oxide as metal-free carbon for adsorption and catalytic oxidation of organics in water

Activation of reduced graphene oxide (RGO) using CO2 to obtain highly porous and metal-free carbonaceous materials for adsorption and catalysis was investigated. A facile one-pot thermal process can simultaneously reduce graphene oxide and produce activated RGO without introducing any solid or aqueous activation agent. This process can significantly increase the specific surface area (SSA) of RGO from 200 to higher than 1200 m2 g-1, and the obtained materials were proven to be highly effective for adsorptive removal of both anionic (phenol) and cationic (methylene blue, MB) organics from water. Moreover, the activated RGO materials exhibited much better activity in effective activation of peroxymonosulfate (PMS) to produce sulfate radicals for oxidative degradation of MB