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

Atomic-level design of CoOH+-hydroxyapatite@C catalysts for superfast degradation of organics via peroxymonosulfate activation

We report a strategy for simultaneous cobalt removal and organic waste decomposition by using mesoporous hydroxyapatite nanoparticles wrapped in uniform carbon layers (HA@C). The in situ formation of CoOH+-HA@C due to ion exchange greatly improved the degradation efficiency by at least one order of magnitude compared to free Co2+

Enhancing Acidic Dye Adsorption by Updated Version of UiO-66

In this study, two improved versions of UiO-66 were successfully synthesised. Modified UiO-66 and UiO-66-Ce were characterised to confirm the integrity of the structure, the stability of functional groups on the surface and the thermal stability. Activated samples were used for removal harmful anionic dye (methyl orange) (MO) from wastewater. Batch adsorption process was relied to investigate the competition between those MOFs for removing MO from aqueous solution. Based on the results, at a higher initial concentration, the maximum MO uptake was achieved by UiO-66-Ce which was better than modified-UiO-66. They adsorbed 71.5 and 62.5 mg g-1 respectively. Langmuir and Freundlich isotherms were employed to simulate the experimental data. In addition, Pseudo first order and Pseudo second order equations were used to describe the dynamic behaviour of MO through the adsorption process. The high adsorption capacities on these adsorbents can make them promised adsorbents in industrial areas

Removal of methylene blue (MB) by bimetallic- metal organic framework

In this study, three improved versions of UiO-66 metal organic frameworks (MOFs) were synthesised successfully: Different ratios of Ca+2/Zr+4 were used to synthesise UiO-66, UiO-66-10%Ca and UiO-66-30%Ca. Batch adsorption experiments were achieved to remove MB from wastewater by UiO-66-Ca. UiO-66-10%Ca exhibited the highest adsorption capacity with maximum  MB adsorption capacity of 15 mg. g–1 in UiO-66-30%Ca while UiO-66 demonstrated lower MB loading. Langmuir and Freundlich models have been employed to describe isotherms. A kinetics study indicated pseudo first-order and pseudo second-order equations. In addition, an intraparticle diffusion model was utilised. The results presented here may facilitate the further enhancement of UiO-66 MOFs and advance the synthesis of multimetal MOFs in future research

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

Nitrogen-doped carbon nanospheres-modified graphitic carbon nitride with outstanding photocatalytic activity

Metals and metal oxides are widely used as photo/electro-catalysts for environmental remediation. However, there are many issues related to these metal-based catalysts for practical applications, such as high cost and detrimental environmental impact due to metal leaching. Carbon-based catalysts have the potential to overcome these limitations. In this study, monodisperse nitrogen-doped carbon nanospheres (NCs) were synthesized and loaded onto graphitic carbon nitride (g-C3N4, GCN) via a facile hydrothermal method for photocatalytic removal of sulfachloropyridazine (SCP). The prepared metal-free GCN-NC exhibited remarkably enhanced efficiency in SCP degradation. The nitrogen content in NC critically influences the physicochemical properties and performances of the resultant hybrids. The optimum nitrogen doping concentration was identified at 6.0 wt%. The SCP removal rates can be improved by a factor of 4.7 and 3.2, under UV and visible lights, by the GCN-NC composite due to the enhanced charge mobility and visible light harvesting. The mechanism of the improved photocatalytic performance and band structure alternation were further investigated by density functional theory (DFT) calculations. The DFT results confirm the high capability of the GCN-NC hybrids to activate the electron–hole pairs by reducing the band gap energy and efficiently separating electron/hole pairs. Superoxide and hydroxyl radicals are subsequently produced, leading to the efficient SCP removal

Platinum single atoms anchored on ultra-thin carbon nitride nanosheets for photoreforming of glucose

Photoreforming of biomass is a fascinating process that harnesses renewable sunlight and biomass to produce hydrogen under ambient conditions, holding a significant promise for future energy sustainability. However, the main challenge lies in developing highly active and stable photocatalysts with high light harvesting efficiency. In this study, we adopted a simple yet effective approach that combines thermal exfoliation and photodeposition to anchor Pt single atoms onto ultra-thin g-C3N4 nanosheets (MCNN). The incorporation of Pt single atoms induced a distinct red-shift in the visible light region, augmenting the solar energy absorption capacity, while the enlarged surface area of g-C3N4 nanosheets improved the mass transfer. Moreover, the enhanced photoelectric properties further contributed to the superior performance of Pt-MCNN-3.0 % in the photoreforming of glucose for hydrogen evolution. Remarkably, Pt-MCNN-3.0 % demonstrated an impressive hydrogen generation rate, approximately 59 times higher than that of MCNN, after a 3 h visible-light irradiation, maintaining a satisfied photo-stability. This work addresses the critical need for design of efficient photocatalysts, bringing us one step closer to realizing the potential of biomass photoreforming as a sustainable and clean energy conversion technology

Visible light responsive titania photocatalysts codoped by nitrogen and metal (Fe, Ni, Ag, or Pt) for remediation of aqueous pollutants

Various cation and nitrogen doped and codoped TiO2 photocatalysts, such as N–TiO2, Pt–TiO2, N–Fe–TiO2, N–Ni–TiO2, N–Ag–TiO2 and N–Pt–TiO2, were prepared by an acid-catalysed sol–gel process. The photocatalysts were characterised by X-ray diffraction (XRD), nitrogen adsorption–desorption isotherms, UV–visible diffuse reflectance absorption spectroscopy (UV–vis DRS), and X-ray photoelectron spectroscopy (XPS). The activities of the photocatalysts were evaluated in photodegradation of phenol solutions under simulated sunlight irradiations. A negative effect of some transition metals (iron and nickel) onphotocatalysis was observed on N-metal codoped TiO2, while enhancements in photocatalysis from noble metals (silver and platinum) were obtained. N–Pt codoped TiO2 showed a higher activity under UV–vis irradiations than Degussa P25, with an enhancement of 5.9 times higher. The synergistic effect of N–Pt-codoping was ascribed to the multivalent states of platinum. In addition, photocatalytic activity of N-, Pt-doped and N–Pt-codoped materials were further investigated under visible light irradiations with lambda > 430 nm and lambda > 490 nm. This study therefore demonstrated a promising strategy for design of highly efficient photocatalysts for remediation of aqueous pollutants