Broad-bandgap porous graphitic carbon nitride with nitrogen vacancies and oxygen doping for efficient visible-light photocatalytic degradation of antibiotics.

Effective degradation methods are required to address the issue of antibiotics as organic pollutants in water resources. Herein, a two-stage thermal treatment method was used to prepare porous graphitic carbon nitride (g-C3N4) modified with nitrogen vacancies and oxygen doping at the N-(C)3 position and deep in the g-C3N4 framework. Compared with bulk g-C3N4 (BCN) (7 ± 1 m2/g), the modified sample (RCN-2h) possesses a larger specific surface area (224 ± 1 m2/g), a larger bandgap (by 0.19 eV), and a mid-gap state. In addition, RCN-2h shows 15.4, 11.2, and 9.5 times higher photodegradation rates than BCN for the degradation of 100% ofloxacin (OFX) (within 15 min), tetracycline (within 15 min), and sulfadiazine (within 35 min), respectively. The RCN-2h catalyst also exhibits superior stability and reusability. Systematic characterization and density functional theory calculations demonstrate that the synergistic effect of the porous structure, nitrogen vacancies, and oxygen doping in RCN-2h provides additional reaction sites, improved charge separation efficiency, and shorter diffusion paths for reactants and photogenerated charge carriers. Trapping experiments reveal that •O2- is the main active species in OFX photodegradation, and a possible photodegradation pathway is identified using liquid chromatography-mass spectrometry. Benefiting from the simplicity of synthesis methods and the superiority of elemental doping, carbon nitride materials with functional synergy have great potential for environmental applications.

Quantum dot-doped CeOx-NiB with modulated electron density as a highly efficient bifunctional electrocatalyst for water splitting.

Development of economical, efficient and durable non-noble metal electrocatalysts for the hydrogen/oxygen evolution reaction (HER/OER) holds great promise, but still faces great challenges. Herein, a strategy of doping metal borides with rare earth metal oxides and introducing silicon carbide (SiC) quantum dots has been explored to develop efficient bifunctional electrocatalysts. A novel electrocatalyst consists of SiC quantum dot-decorated CeOx-NiB supported on nickel foam via a one-step mild electroless plating reaction (denoted as CeOx-NiB/SiC@NF). Notably, the modulated electron density of the CeOx-NiB/SiC@NF electrode significantly boosts the electrochemically active surface area and electron transfer, and optimizes the hydrogen/water absorption free energy, which delivers current densities of 50 mA cm-2 and 10 mA cm-2 at overpotentials of only 131 mV and 234 mV for the HER and the OER, respectively. The target electrode requires only 1.43 V to provide 10 mA cm-2 for overall water splitting in 1.0 M KOH. Moreover, the electrode also exhibits good stability and durability at the industrial-grade current density (0.5-1 A cm-2). This work provides a new idea for the development of efficient and durable non-precious metal catalysts.

Electronically modulated nickel boron by CeOx doping as a highly efficient electrocatalyst towards overall water splitting.

Exploiting economic, efficient and durable non-noble metal electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is promising, but still faces enormous challenges. Herein, the strategy of doping a metal boride with a rare earth metal oxide has been explored to develop a highly efficient bifunctional electrocatalyst. The novel electrocatalyst CeOx-NiB consists of CeOx-doped NiB supported on nickel foam, and was fabricated by a one-step mild electroless plating reaction. Remarkably, the CeOx-NiB@NF electrode delivers a current density of 10 mA cm-2 at overpotentials of only 19 mV and 274 mV for the HER and OER, respectively. Two-electrode electrolyzers with the CeOx-NiB@NF electrode require only 1.424 V to deliver 10 mA cm-2 for overall water splitting in 1.0 M KOH, outperforming the Pt-C/NF∥IrO2/NF electrolyzer. Meanwhile, the electrode also has good stability (can work for 100 hours at 10 mA cm-2) and industrial-grade current density. This work provides a new idea for the development of efficient and durable non-precious metal catalysts.

Microwave-assisted chemical recovery of glass fiber and epoxy resin from non-metallic components in waste printed circuit boards.

An efficient, microwave-assisted chemical recovery approach for epoxy resin and glass fiber from non-metallic components (NMC) in waste printed circuit boards (WPCBs) for resource reutilization was developed in this research. HNO3 was selected as the chemical reagent because epoxy resin has low corrosion resistance to HNO3. The influence of reaction parameters such as reaction time, temperature, concentration of HNO3, liquid-solid ratio, and power of the microwave synthesizer on the separation efficiency of NMC (epoxy resin and glass fiber) and the reaction mechanism were investigated. The physical and chemical properties of NMC, reaction solvent, and decomposed products were analyzed using energy dispersive X-ray Spectroscopy (SEM-EDX) and Fourier transform infrared spectroscopy (FT-IR). The results showed that up to 88.42% of epoxy resin and glass fiber ((5 g) 10 mL/g) could be separated under the action of 300 W microwave power at 95 ℃ for 12 h and a HNO3 concentration of 7 mol/L. During the reaction, C-N bonds formed by the crosslinking agent and the three-dimensional network structure of the thermosetting epoxy resin were destroyed. The carbon chain structure and chemical properties of epoxy resin did not change significantly and the functional groups of ethyl acetate maintained the chemical structure before and after the reaction. This uncomplicated and efficient inorganic acid chemical microwave-assisted process holds promise for use as a feasible recovery technology for epoxy resin and glass fibers in NMC. The proposed process is particularly appealing because of its high selectivity, considerable economic advantages, and environmental benefits.

Dissolution and separation of non-metallic powder from printed circuit boards by using chloride solvent.

Non-metallic components (NMC) in waste printed circuit boards (WPCBs) are made of the thermosetting epoxy resin and glass fiber, which has been a research concern in the waste recycling area. The recycling of thermosetting epoxy resin is a serious challenge due to their permanent cross-linked structure. An efficient approach to chemical recycling of epoxy resin for resource reutilization was developed in this research. ZnCl2/CH3COOH aqueous solution was selected as catalysts system to decompose epoxy resin under a mild reaction condition. The influence of reaction parameters such as reaction temperature, time, liquid-solid ratio and ZnCl2 amount on the decomposition efficiency of epoxy resin and reaction mechanism were investigated. The physical and chemical properties of NMC, reaction solvent and decomposed products were analyzed using scanning electron microscope(SEM), Fourier transform infrared spectroscopy (FT-IR) and Gas chromatography-mass spectrometry (GC-MS). Results showed that up to 81.85% of epoxy resin could be dissolved by using a temperature of 190 °C during 8 h with a mixture of acetic acid (15 wt%): ZnCl2 (5 g) 20 mL/g. Incompletely coordinated zinc ions enables the cleavage of CN, CBr and CO bonds in the thermosetting brominated epoxy resin, which was mainly converted to phenol, 2-Bromophenol and 2, 4-Dibromophenol with high resource value. And the functional groups of ethyl acetate and acetic acid maintained chemical structure before and after reaction. This research provided a practical approach to the dissolution and reutilization of NMC in WPCBs.

Mechanochemical treatment of Cr(VI) contaminated soil using a sodium sulfide coupled solidification/stabilization process.

In this research, mechanochemical reduction was carried out to remediate Cr(VI) contaminated soil, and the reduction effectiveness was evaluated by analyzing the corresponding leachable fraction obtained through the toxicity characteristic leaching procedure (TCLP) proposed by the EPA. The results indicated that mechanochemical reduction can efficiently reduce the Cr(VI) concentration in the leachate. Under a milling time of 2 h, milling speed of 500 rpm, ball-to-powder weight ratio of 14 and Na2S dosage of 5%, the Cr(VI) leaching concentration significantly decreased from 663.98 mg L-1 to 0.84 mg L-1, much lower than the regulatory limit of 5 mg L-1. In addition, the significant decrease in Cr(VI) was mainly due to the reduction of Cr(VI) to Cr(III), as supported by X-ray photoelectron spectroscopy (XPS). The mechanochemical reduction with mechanism proposed in this experiment may involve two major processes: solidification and reduction (stabilization).