Highly Active Heterogeneous Fenton-like System Based on Cobalt Ferrite

Coactivation of Hydrogen Peroxide Using Pyrogenic Carbon and Magnetite for Sustainable Oxidation of Organic Pollutants

Pyrogenic carbon and magnetite (Fe3O4) were mixed together for the activation of hydrogen peroxide (H2O2), aiming to enhance the oxidation of refractory pollutants in a sustainable way. The experimental results indicated that the straw-derived carbon obtained by pyrolysis at 500-800 °C was efficient on coactivation of H2O2, and the most efficient one was that prepared at 700 °C (C700) featured with abundant defects. Specifically, the reaction rate constant (kobs) for removal of an antibiotic ciprofloxacin in the coactivation system (C700/Fe3O4/H2O2) is 12.5 times that in the magnetite-catalyzed system (Fe3O4/H2O2). The faster pollutant oxidation is attributed to the sustainable production of •OH in the coactivation process, in which the carbon facilitated decomposition of H2O2 and regeneration of Fe(II). Besides the enhanced H2O2 utilization in the coactivation process, the leaching of iron was controlled within the concentration limit in drinking water (0.3 mg·L-1) set by the World Health Organization.

Cobalt ferrite as an electromagnetically boosted metal oxide hetero-Fenton catalyst for water treatment

The cobalt ferrite Fenton catalysts were obtained by the flow co-precipitation method. FTIR, XRD, and Mössbauer spectroscopy confirmed the spinel structure. The crystallite size of the as-synthesized sample is 12 nm, while the samples annealed at 400 and 600 °C have crystallite sizes of 16 and 18 nm, respectively. The as-synthesized sample has a grain size of 0.1-5.0 μm in size, while the annealed samples have grain sizes of 0.5 μm-15 μm. The degree of structure inversion ranges from 0.87 to 0.97. The catalytic activity of cobalt ferrites has been tested in the decomposition of hydrogen peroxide and the oxidation of caffeine. The annealing of the CoFe₂O₄ increases its catalytic activity in both model reactions, with the optimal annealing temperature being 400 °C. The reaction order has been found to increase with increasing H₂O₂ concentration. Electromagnetic heating accelerates the catalytic reaction more than 2 times. As a result, the degree of caffeine decomposition increases from 40% to 85%. The used catalysts have insignificant changes in crystallite size and distribution of cations. Thus, the electromagnetically heated cobalt ferrite can be a controlled catalyst in water purification technology.

Simple preparation of a CuO@γ-Al2O3 Fenton-like catalyst and its photocatalytic degradation function

We designed a photocatalyst and developed sustainable wastewater purification technology, which have significant advantages in effectively solving the global problem of drinking water shortage. In this study, a new nanocomposite was reported and shown to be a catalyst with excellent performance; CuO was coated successively onto functionalized nano γ-Al₂O₃, and this novel structure could provide abundant active sites. We evaluated the performance of the CuO@γ-Al₂O₃ nanocomposite catalyst for polyvinyl alcohol (PVA) degradation under visible light irradiation. Under optimized conditions (calcination temperature, 450 °C; mass ratio of γ-Al₂O₃:Cu(NO₃)₂·3H₂O, 1:15; pH value, 7; catalyst dosage, 2.6 g/L; reaction temperature, 20 °C; and H₂O₂ dosage, 0.2 g/mL), the CuO@γ-Al₂O₃ nanocomposite catalyst presented an excellent PVA removal rate of 99.21%. After ten consecutive degradation experiments, the catalyst could still maintain a PVA removal rate of 97.58%, thus demonstrating excellent reusability. This study provides an efficient and easy-to-prepare photocatalyst and proposes a mechanism for the synergistic effect of the photocatalytic reaction and the Fenton-like reaction.

Quantification of 2-chlorohydroquinone based on interaction between N-doped carbon quantum dots probe and photolysis products in fluorescence system

As a member of chlorophenolic compounds, 2-chlorohydroquinone (H₂QCl) has been widely used as intermediates in various chemical industries and leaded to serious threat on the environment. It is urgent to develop simple and robust analytical method for sensitive and selective determination of H₂QCl. Carbon quantum dots (CQDs), a promising photoluminescence nanomaterial, have gained sufficient concern as optical sensors owing to their outstanding photochemical properties. In this work, nitrogen doped carbon quantum dots (N-CQDs) were successfully synthesized by a simple secondary hydrothermal method and applied as a fluorescent probe for the quantitation of H₂QCl. A new fluorescence region centered at excitation wavelength of 310 nm and emission wavelength of 390 nm appeared after nitrogen doping. It was found that the N-CQDs exhibited a high selectivity towards H₂QCl with sensitive fluorescence response and the fluorescence quenching of N-CQDs was linear with the concentration of H₂QCl in the range of 30-90 μM (Y = 0.0049X + 0.1255, R² = 0.996). This is the first time that the dual role of excitation light was observed in the fluorescence detection system. The ultraviolet light acted as not only the excitation energy source for N-CQDs photoluminescence, but also the light source for photolysis of H₂QCl. In the detection process, H₂QCl was degraded to p-benzoquinone by light, and then the CQDs combined with p-benzoquinone through Michael addition reaction under the action of doped nitrogen. The electron transfer from N-CQDs to the linked p-benzoquinone caused the quenching of fluorescence originated from the edge state of N-CQDs. Furthermore, this established method can be applied for the quantitative determination of H₂QCl in environmental water samples with satisfactory recoveries between 94.31 and 105.51%.