The compound p-Nitrophenol (p-NP) is widely recognized as a highly toxic nitro-aromatic substance that urgently requires emission control. Reducing p-NP to p-aminophenol (p-AP) not only decreases its toxicity and mineralization properties in nature but also provides a key raw material for the chemical and pharmaceutical industries. The study used coal fly ash (CFA) as a catalyst carrier for synthesizing the p-NP reduction catalyst. Using CFA as an alternative option not only reduces costs but also achieves the objective of treating waste with waste compared to utilizing commercial solid materials for synthesizing catalysts. By employing hydrochloric acid and sodium hydroxide pretreatment methods, the physicochemical properties of CFA are significantly improved, enhancing the dispersion of palladium (Pd) nanoparticles. The structural features of the prepared samples were characterized using various surface analysis techniques, and both intermittent and continuous modes were experimentally tested for the model catalytic reaction involving the sodium borohydride (NaBH₄)-mediated reduction of p-NP. The results demonstrate that CFA has potential in wastewater treatment.

Fly ash, a type of solid waste generated in power plants, can be utilized as a catalyst carrier to enhance its value-added potential. Common methods often involve using a large amount of alkali for preprocessing, resulting in stable quartz and mullite forming silicate dissolution. This leads to an increased specific surface area and pore structure. In this study, we produced a catalyst composed of MnO_x/NiOOH supported on fly ash by directly employing nickel hydroxide and potassium permanganate to generate metal active sites over the fly ash surface while simultaneously creating a larger specific surface area and pore structure. The ozone catalytic oxidation performance of this catalyst was evaluated using sodium acetate as the target organic matter. The experimental results demonstrated that an optimal removal efficiency of 57.5% for sodium acetate was achieved, surpassing even that of MnO_x/NiOOH supported catalyst by using γ-Al₂O₃. After loading of MnO_x/NiOOH, an oxygen vacancy is formed on the surface of fly ash, which plays an indirect oxidation effect on sodium acetate due to the transformation of ozone to •O₂⁻ and •OH over this oxygen vacancy. The reaction process parameters, including varying concentrations of ozone, sodium acetate, and catalyst dosage, as well as pH value and the quantitative analysis of formed free radicals, were examined in detail. This work demonstrated that fly ash could be used as a viable catalytic material for wastewater treatment and provided a new solution to the added value of fly ash.