High-Performance Graphene/Carbon Nanotube-Based Adsorbents for Treating Diluted o-Cresol in Water in a Pilot-Plant Scale Demo

Graphene/carbon nanotube (CNT)-based adsorbents were fabricated on a kilogram scale by extrusion processing (where graphene is used as the major adsorption material and CNTs make up the backbone to enhance the mechanical strength) and then mixed and bonded with poly(tetrafluoroethylene). Kilogram-scale adsorbents were used to treat the content of o-cresol in wastewater to be <1.12 mg/kg in a continuous and reversible adsorption-desorption apparatus, which could last for 99 h with a space velocity of 30 h^-1 and a total wastewater capacity of 5 tons per day. Brunauer-Emmett-Teller (BET), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and Raman spectroscopy all suggested that the surface properties and pore structure of the spent adsorbents remain unchanged after recycling at both low-temperature adsorption and high-temperature desorption in vacuum. These results provided an effective reversible adsorbent system for removing aromatic organics and prompted the scaled-up applications of carbon nanomaterials in the treatment of wastewater.

Converting Organic Wastewater into CO Using MOFs-Derived Co/In2O3 Double-Shell Photocatalyst

The photocatalytic conversion of organic wastewater into value-added chemicals is a promising strategy to solve the environmental issue and energy crisis. Herein, Co/In₂O₃ nanotubes with a double-shell structure, as a highly efficient photocatalyst, are synthesized by a one-step calcination method. The Co/In₂O₃ heterostructure shows an outstanding photocatalytic CO₂ reduction performance of 4902 μmol h^-1 g^-1. Notably, these Co/In₂O₃ photocatalysts also achieve CO₂ self-generation and in situ reduction conversion in acid organic wastewater (phenol solution), in which the high CO₂ (47.5 μmol h^-1 g^-1) and CO (0.9 μmol h^-1 g^-1) evolution rates are demonstrated under solar irradiation. Transient photovoltage (TPV) tests demonstrate that Co nanoparticles on Co/In₂O₃ double-shell heterostructure serve as the CO₂ reduction sites for the effective capture and stabilization of the photogenerated electrons.

The Application of Carbon Nanotube/Graphene-Based Nanomaterials in Wastewater Treatment

The treatment of organic wastewater is of great significance. Carbon nanotube (CNT)/graphene-based nanomaterials have great potential as absorbent materials for organic wastewater treatment owing to their high specific surface area, mesoporous structure, tunable surface properties, and high chemical stability; these attributes allow them to endure harsh wastewater conditions, such as acidic, basic, and salty conditions at high concentrations or at high temperatures. Although a substantial amount of work has been reported on the performance of CNT/graphene-based nanomaterials in organic wastewater systems, engineering challenges still exist for their practical application. Herein, the adsorption mechanism of CNT- and graphene-based nanomaterials is summarized, including the adsorption mechanism of CNTs and graphene at the atomic and molecular levels, their hydrophilic and hydrophobic surface properties, and the structure-property relationship required for adsorption to occur. Second, the structural modification and recombination methods of CNT- and graphene-based adsorbents for various organic wastewater systems are introduced. Third, the engineering challenges, including the molding of macroscopically stable adsorbents, adsorption isotherm models and adsorption kinetic behaviors, and reversible adsorption performance compared to that of activated carbon (AC) are discussed. Finally, cost issues are discussed in light of scalable and practical application of these materials.

Nanostructure Design and Catalytic Performance of Mo/ZnAl-LDH in Cationic Orchid X-BL Removal

The nanostructure of ZnAl-layered double hydroxide (ZnAl-LDH) was designed to promote the catalytic performance of Mo-based ZnAl-LDH (Mo/ZnAl-LDH) catalysts, in a catalytic wet air oxidation (CWAO) process, under room temperature and pressure, in degradation of dye wastewater. Four most commonly used preparation methods, traditional precipitation (TP), hydrothermal synthesis (HS), sol-gel (SG), and urea co-precipitation (UC) were employed to prepare the ZnAl-LDH. The resulting Mo/ZnAl-LDH samples were contrasted through surface area, crystal structure, chemical state, and morphology. The degradation of cationic orchid X-BL, under room temperature and pressure, was developed to determine the catalytic activity of these Mo/ZnAl-LDH samples. The results showed that the nanostructure of ZnAl-LDH, prepared by HS, enhanced the adhesion of the catalytic active component, thus Mo/ZnAl-LDH had the highest catalytic activity of 84.2% color removal efficiency and 73.9% total organic carbon removal efficiency. Specific Mo species, such as Na₂Mo₂O₇, Mo dispersion, and O^2- ions were proved to be related with catalytic performance. These findings preliminarily clarified that LDHs preparation methods make a difference in the performance of Mo/LDHs.