The doping of multiple heteroatoms can improve the electrochemical properties of carbon substrates. However, in existing studies, carbon, iron and nitrogen sources are generally mixed directly and then pyrolyzed for secondary activation. This tends to form aggregates of metal particles or metal oxides and requires the consumption of large amounts of alkali and energy. Therefore, there is an urgent need to develop an environmentally friendly technology capable of uniformly doping iron and nitrogen into carbon materials. In this work, porous Fe-N-C composites were prepared at 600°C using potassium humate (HA-K) obtained from cotton straw by low-temperature pyrolysis as the carbon source, and urea-iron complexes formed by the pre-coordination of urea and Fe as the iron and nitrogen sources. In the absence of secondary activation, the best sample Fe-NHPC-2 had a good mesoporous structure with high specific surface area (889. 01 m2 g−1). It had a high specific capacitance of 256.8 F g−1 at a current density of 0.5 A g−1. The capacitance retention was 92.6% after 10,000 cycles at a current density of 10 A g−1. In the symmetric supercapacitor application, the energy density reached 33.16 Wh kg−1 when the power density was 600.2 W kg−1.
A new adsorbent with chromium removal function was synthesized by carbon thermal method using iron-containing waste Fenton sludge and carbon-containing solid waste fly ash to treat high pH scoring wastewater generated from industrial processes. The results showed that the adsorbent used T = 273.15 K, pH = 10, t = 1200 min, C0 = 100 mg/L, had a removal rate of Cr(VI) of more than 80%, and the adsorption capacity could reach 393.79 mg/g. The characterization results show that the synthesized mesoporous nitrogen-doped composite material has a large specific surface area and mesoporous structure, and the surface of the material is rich in oxygen-containing functional groups and active sites. Compared with other studies, the adsorption capacity of the material is larger, which indicates that the removal effect of Cr(VI) in this study is better. The adsorption kinetic results show that the adsorption follows a pseudo second kinetic model, and the adsorption process is a chemisorption involving electron sharing or electron exchange. This experiment designed a simple method to synthesize mesoporous nitrogen-doped composites using industrial solid waste, with raw materials from cheap and easily available industrial solid waste, and solved the dual problems of heavy metals in wastewater and solid waste, providing a new idea for the resource utilization of Fenton sludge while not producing secondary pollution.
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