Water disinfection using hydrogen peroxide with fixed bed hematite catalyst - kinetic and activity studies.

A lab-scale reactor with a fixed-bed hematite catalyst for the effective decomposition of H2O2 and bacteria inactivation was designed. The bactericidal effect is the largest at a low initial bacterial count of 2·103 CFU/L, which is typical for natural surface waters. When using a 5 mM H2O2 solution and a residence time of 104 min, the reduction in the number of E. coli bacteria is about 3.5-log. At a higher initial bacterial count of 1-2·104 CFU/L, a 5 mM H2O2 solution reduces the bacteria number by about 4-log. The H2O2 decomposition follows the log-linear kinetics of a first-order reaction while the bacterial inactivation does not. The kinetics of bacterial inactivation was described using the Weibull model in the modified form: log10(N0/N) = b · tn. The values of the non-linearity parameter n were found to be lower than 1, indicating that bacterial inactivation slows down over time. With increasing initial H2O2 concentration, the rate parameter b increases while the non-linearity parameter n decreases. With increasing temperature, both parameters increase. The stability of the catalyst has been proved by XRD, FTIR, SEM, and ICP-OES. The concentration of iron leaching into water during disinfection is much lower than the limit declared by WHO for iron in drinking water. The results show that technical-grade hematite is a promising Fenton-like catalyst for water disinfection. The fixed-bed reactor can be the basis of the mobile installations for water purification in emergencies.

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.

Eco-friendly synthesis of cobalt-zinc ferrites using quince extract for adsorption and catalytic applications: An approach towards environmental remediation.

Cobalt-zinc ferrite nanoparticles were synthesized using environmentally friendly approach with quince extract as a reducing agent. Crystal structure and morphology of the obtained materials were studied by XRD, SEM-EDS, Mössbauer and IR spectroscopy. The synthesized nanoparticles have a cubic spinel structure and crystallite size ranging from 5 to 9 nm. The infrared spectra contain characteristic absorption bands for the MA-O (∼560 cm-1) and MB-O bonds (∼420 cm-1). Force constants were calculated for both tetrahedral and octahedral bonds. As the Co content increases, the force constant for the tetrahedral bond increases and the force constant for the octahedral bond decreases. The obtained ferrite nanoparticles have good magnetization as shown by VSM (in the range from 36 to 67 emu/g). Magnetic nanoparticles CoxZn1-xFe2O4 were also tested for induction heating with electromagnetic field. The sample with x (Co) = 0.4 has the highest specific absorption rate. The synthesized samples were tested as adsorbents using the Congo Red dye as model pollutant. The best adsorbent was pure zinc ferrite with the adsorption capacity of 24.7 mg/g. The catalytic activity of the obtained ferrites for the decomposition of H2O2 was studied as well. The most active catalyst was pure cobalt ferrite. Probably, the active centers are octahedral cobalt ions. Thus, the obtained magnetic nanoparticles can be used for the adsorptive removal of pollutants, catalytic decomposition of the H2O2 and low-frequency hyperthermia.

Optimization of TiO2-P25 photocatalyst dose and H2O2 concentration for advanced photo-oxidation using smartphone-based colorimetry.

Color images taken by a smartphone camera were used to estimate the rate of advanced photo-oxidation reaction of Direct Red 23 (DR23) azo dye as a model organic pollutant. The red, green, blue color coordinates were tested to quantify the dye. Images of the reaction mixture were taken at specified intervals to obtain kinetic lines and reaction rate constants. Both the reaction rate constant and the final degree of degradation were plotted as functions of the photocatalyst dose and the concentration of H2O2. The smartphone measurements are fully consistent with the reference spectrophotometry data. The maximum degradation efficiency of the DR23 dye was recorded at C0(H2O2) = 2.5 mM and photocatalyst dose equal to 1.0 mg/L. Higher H2O2 concentrations reduce the degradation rate as a result of the side reaction of H2O2 with OH radicals. A two-factor experimental design was used to study the effects of photocatalyst dose and H2O2 concentration with five and seven levels, respectively. The analysis of variance results indicated that the concentration of H2O2 had the greater influence. The smartphone provides quick and easy measurement of the photodegradation rate directly in the solutions without sampling. The proposed approach can be applied under field conditions in wastewater treatment plants.