Yajun Ji

Both hazardous waste and emerging pollutants pose harm to ecological integrity and public health. The management has emerged as major challenges and research hotspots within the environmental sector. Herein, highly active Fe-doped carbon nitride catalysts were fabricated by optimizing the ratio of waste toner to melamine in the feedstock via a one-step co-pyrolysis process. The prepared catalyst featured a hollow nanotube structure, with a large SBET (92.06 m2/g), plentiful N- and Fe-containing active sites, and good magnetism. When the ratio of waste toner to melamine in the raw materials was 1: 4, the obtained catalyst (WTM-1/4) demonstrated the highest performance in activating PMS for TC elimination. In WTM-1/4/PMS system, 87% of TC was removed in 10 min, yielding a high kobs of 1.2 min-1. Moreover, the WTM-1/4/PMS system could effectively remove TC from water even under varying pH conditions or with coexisting ions, indicating its great potential for treating practical organic wastewater. Mechanistic studies revealed that TC in WTM-1/4/PMS system was eliminated via electron transfer, radical and non-radical pathways. Specifically, the active sites including Fe0, graphitic N, and pyridinic N/Fe-Nx in WTM-1/4, activated PMS to generate reactive species like 1O2 and FeIV=O, which effectively degrade TC. Most of the intermediate products pose reduced environmental risks. Consequently, this study proposes a straightforward strategy that not only promotes resource recovery of waste toner but also employs the derived catalyst for efficient TC degradation in water, achieving the effect of killing two birds with one stone.

Utilizing the pyrolysis reaction of endothermic hydrocarbon fuels to provide thermal protection for hypersonic vehicles is a feasible approach. The introduction of catalysts or cracking-initiating additives could promote hydrocarbon fuel cracking and increase the reaction heat sink. Catalysts such as ZSM-5 zeolite, Al₂O₃, and precious metals were commonly used for hydrocarbon fuel cracking. By optimizing their pore structure and acidity, their catalytic cracking performance can be effectively improved. These catalysts can function not only as catalytic coatings but also be dispersed in the fuel to act via quasi-homogeneous catalytic cracking. Additionally, small-molecule and macromolecular additives could crack at lower temperatures to generate active free radicals, thereby initiating the cracking of hydrocarbons and increasing the reaction heat sink. Under the conditions of a reaction temperature of 650–750 °C, a pressure of 3–5.5 MPa, and a fuel flow rate of 1 g/s, quasi-homogeneous catalysts can enhance the heat sink of hydrocarbon fuel cracking by 5–21%, while cracking-initiating additives can enhance it by 5.6–8.6%. Therefore, based on the different action modes of catalysts or additives, this review summarizes the recent research on improving the cracking of endothermic hydrocarbons from three aspects: coating catalysts, quasi-homogeneous catalysts, and cracking-initiating additives. Subsequently, the potential challenges of each approach in practical applications are analyzed. Furthermore, based on the current research findings, we outline future research directions with the expectation of facilitating the advancement of efficient cracking technologies for endothermic hydrocarbons.

Heterogeneous catalytic degradation of organic dyes can effectively achieve the goals of reducing the chromaticity of aqueous solutions and completely removing pollutants. We here present a carbon-nitride-wrapped zero-valent Fe catalyst (CNFe), which can directly degrade Acid Red G (ARG) dye without additional oxidants. CNFe exhibited a nanotube-like morphology, wherein the zero-valent Fe (Fe⁰) was wrapped by a carbon layer to effectively enhance its dispersibility and prevent its oxidative deactivation. Meanwhile, the large specific surface area (169.19 m²/g), along with abundant active sites such as Fe and O, endowed CNFe with excellent activity. Under strongly acidic conditions, even in the presence of various anions, CNFe can still remove approximately 91.6% of ARG within 30 min. In a 10 h continuous flow column experiment, the removal efficiency of ARG consistently exceeded 67.6%, indicating that CNFe had great potential for treating actual dyeing wastewater. Catalytic mechanism studies showed that, under neutral conditions, CNFe mainly removed ARG through adsorption, whereas, under acidic conditions, the Fe⁰ in CNFe can not only activate molecular oxygen to generate HO· for the oxidative degradation of ARG but also remove ARG via reduction. Furthermore, CNFe can adsorb ARG through hydrogen bonding of surface hydroxyl groups. The developmental toxicity of the generated intermediates was effectively reduced, demonstrating lower environmental risks. Therefore, this study provided a simple, high-efficiency, and economical method for removing dyes from water, which can offer guidance for the treatment of practical dye wastewater.

Pruned tea leaves are discarded or burned as agricultural residue, causing resource waste and serious environmental problems. Pruned tea leaves with a rich number of cellulosic and polyphenolic components could be used as biomass feedstocks and reducing agents to synthesize ZVI-embedded biochar. In this work, a green, inexpensive and convenient method was developed for the synthesis of nanoscale zero-valent iron embedded biochar (TLBC-nZVI) using pruned tea leaves. TLBC-nZVI showed excellent performance in Cr(VI) removal (166.65 mg g−1) from aqueous solutions. Isothermal, kinetic and thermodynamic studies showed that Cr(VI) removal fit well with the Freundlich model and pseudo-second order model. Additionally, the removal process was a chemical, spontaneous and endothermic reaction. The removal mechanisms were as follows: (i) protonated TLBC-nZVI adsorbed anionic Cr(VI) by electrostatic interaction under acidic conditions; (ii) Fe0, Fe(II) and some surface functional groups (such as –NH2 and –OH) reduced Cr(VI) to Cr(III); and (iii) Cr(III) was removed through complexation, physical adsorption and coprecipitation.