Effect of supporting electrolytes in electrochemically-assisted photodegradation of an azo dye

Impact of water matrices on oxidation effects and mechanisms of pharmaceuticals by ultraviolet-based advanced oxidation technologies: A review

The binding between water components (dissolved organic matters, anions and cations) and pharmaceuticals influences the migration and transformation of pollutants. Herein, the impact of water matrices on drug degradation, as well as the electrical energy demands during UV, UV/catalysts, UV/O₃, UV/H₂O₂-based, UV/persulfate and UV/chlorine processes were systemically evaluated. The enhancement effects of water constituents are due to the powerful reactive species formation, the recombination reduction of electrons and holes of catalyst and the catalyst regeneration; the inhibition results from the light attenuation, quenching effects of the excited states of target pollutants and reactive species, the stable complexations generation and the catalyst deactivation. The transformation pathways of the same pollutant in various AOPs have high similarities. At the same time, each oxidant also can act as a special nucleophile or electrophile, depending on the functional groups of the target compound. The electrical energy per order (EEO) of drugs degradation may follow the order of EEO_UV > EEO_UV/catalyst > EEO_UV/H2O2 > EEO_UV/PS > EEO_UV/chlorine or EEO_UV/O3. Meanwhile, it is crucial to balance the cost-benefit assessment and toxic by-products formation, and the comparison of the contaminant degradation pathways and productions in the presence of different water matrices is still lacking.

Synthesis of nZnO from waste batteries by hydrometallurgical method for photocatalytic degradation of organic pollutants under visible light irradiation

Waste zinc carbon (Zn-C) batteries are generated worldwide in a large amount. They are non-rechargeable and costly to recycle. Therefore, they end up in the landfills where they create hazards for humans and for environment as well. Zn-C batteries are rich in concentration of different heavy metals so they can be subjected for the recovery of metals for the development of valuable new materials. In this study authors have proposed an easy hydrometallurgical method for the recovery of zinc from waste Zn-C batteries to synthesize nano zinc oxide (nZnO) photocatalyst. The prepared nZnO particles were irregular in shape, highly crystalline in nature with crystallite size 23.94 nm. The band gap of the photocatalyst was 3.1 eV. The photocatalytic activity of the synthesised nZnO was tested for the degradation of three organic pollutants namely; phenol, p-nitrophenol (PNP) and crystal violet dye (CV) in an aqueous solution under visible light irradiation. nZnO showed a good catalytic efficiency for the degradation of all the three pollutants, however, the crystal violet (CV) removal was best in comparison with the other pollutants, it was minimally effected by the increase in CV concentration. The maximum degradation of phenol, PNP and CV was found to be 95.03 ± 0.2%, 88.63 ± 0.1% and 97.87 ± 0.4%, respectively. The degradation data was fitted best with pseudo-first-order kinetic model. The photocatalyst was recyclable and its regeneration ability was higher for initial three cycles. The intermediate compounds formed in the process of degradation were determined by liquid chromatography and mass spectroscopy (LC-MS) analysis.

The effects of the supporting electrolyte on the simultaneous determination of vitamin B2, vitamin B6, and vitamin C using a modification-free screen-printed carbon electrode

A simple and modification-free SPCE demonstrated high efficiency for the simultaneous detection of VB₂, VB₆, and VC in various practical applications.

Enhancing photocatalytic degradation of methyl orange by crystallinity transformation of titanium dioxide: A kinetic study

This work aimed to enhance the photocatalytic degradation of methyl orange (MO) by crystallinity transformation of titanium dioxide (TiO₂ ). In addition, the kinetic degradation of MO was determined. To transform its crystallinity, TiO₂ was synthesized using a sol-gel method and calcined at between 200°C to 600°C. Calcination at a temperature of 250°C resulted in TiO₂ that showed the best performance, corresponding to MO removal of 87% ± 7%. MO removal by TiO₂ calcined between 250°C to 400°C was higher than for commercial TiO₂ powder (Sigma-aldrich) (62% ± 4%). TiO₂ with a small crystallite size and high anatase fraction enhanced the photocatalytic degradation of MO, while the specific surface area and surface roughness seemed to play a minor role. The photocatalytic degradation of MO was NaCl-independent, while the photocatalytic activity increased with decreased pH. Reused TiO₂ showed similar photocatalytic degradation of MO compared with pristine TiO₂ , at 84 ± 2%. The oxidation kinetics of TiO₂  calcined at 250°C were fitted to the Langmuir-Hinshelwood model (R²  = 0.9134). The k_r and K_s values were 0.027 mg L^-1  min^-1  and 0.621 L/mg, respectively. Crystallinity transformation was a major factor in the enhancement of photocatalytic degradation of MO. PRACTITIONER POINTS: Photocatalytic activity of TiO₂ depends on calcination temperature, pH, and a number of UVC lamps. TiO₂ with a small crystallite size and high anatase fraction enhanced the photocatalytic degradation of MO.

Evaluation of photocatalytic fuel cell (PFC) for electricity production and simultaneous degradation of methyl green in synthetic and real greywater effluents

Recycling of alternative water sources particularly greywater and recovery of energy from wastewater are gaining momentum due to clean water scarcity and energy crisis. In this study, the photocatalytic fuel cell (PFC) employing ZnO/Zn photoanode and CuO/Cu photocathode was successfully designed for effective greywater recycling as well as energy recovery. The photoelectrodes were analyzed using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) and fourier transform infrared (FTIR) spectroscopy. The PFC performance in terms of electricity generation and parallel methyl green (MG) degradation were evaluated under operating parameters such as electrolyte type, initial MG concentration and solution pH. The results showed that the addition of Na₂SO₄ electrolyte, MG concentration of 40 mg L^-1 and solution pH of 5.2 improved the short circuit current density (J_sc) and power density (P_max) in the as-constructed PFC. Such a system also afforded highest MG and chemical oxygen demand (COD) removal efficiencies after 4 h of irradiation. The photoanodes used in this study demonstrated great recyclability after four repetition tests. The COD removal was reduced to some extents when the PFC treatment was tested in the real greywater under optimal conditions. Various greywater quality parameters including ammoniacal nitrogen (NH₃-N), turbidity, pH and biochemical oxygen demand (BOD₅) were also monitored. The phytotoxicity experiments via Vigna radiate seeds indicated a reduction in the phytotoxicity.

Photodegradation of Sulfadiazine in Aqueous Solution and the Affecting Factors

Knowledge about photochemical behavior of sulfonamides under UV light is limited. In this study, photodegradation of sulfadiazine in water by ultraviolet (UV) light was studied using a 300 W, 365 nm UV lamp. The degradation process followed well the first-order kinetics, with a half-life of 9.76 min in water with air saturation. The photodegradation was slower at acidic pH 4.52 than at pH 6.98 and pH 8.90. Addition of H2O2and nitrate enhanced the photodegradation rate, while addition of ethanol, nitrite, sulfate, and bicarbonate depressed the reaction rate. This study suggested that sulfadiazine photodegradation under UV light is generally favored by the attack of hydroxyl radicals.

Parameters effect on heterogeneous photocatalysed degradation of phenol in aqueous dispersion of TiO2

Photocatalytic degradation of phenol selected as model compound of organic pollutant had been investigated in aqueous titanium dioxide (TiO2) dispersion under UV irradiation. The effects of various parameters such as pH, catalyst concentration, phenol concentration, anions, metal ions, electron acceptors, and surfactants on the photocatalytic degradation of phenol were investigated. The degradation kinetics was determined by the change in phenol concentration employing UV-Vis spectrometry as a function of irradiation time. The degradation kinetics of phenol follows pseudo first-order kinetics. The results showed a significant dependence of the photocatalytic degradation of phenol on the functional parameters. The probable promising roles of the additives on the degradation process were discussed.

Electrochemical-assisted photodegradation of mixed dye and textile effluents using TiO2 thin films

Mixed dye consists of six commercial dyes and textile effluents from cotton dyeing process were treated by electrochemical-assisted photodegradation under halogen lamp illumination. Two types of effluents were collected which are samples before and after undergone pre-treatment at the factory wastewater treatment plant. The photodegradation process was studied by evaluating the changes in concentration employing UV-vis spectrophotometer (UV-vis) and total organic carbon (TOC) analysis. The photoelectrochemical degradation of mixed dye was found to follow the Langmuir Hinshelwood pseudo-first order kinetic while pseudo-second order kinetic model for effluents by using TOC analyses. The chemical oxygen demand (COD) and biochemical oxygen demand (BOD) values of mixed dye and raw effluents were reported. Photoelectrochemical characteristic of pollutants was studied using the cyclic voltammetry technique. Raw effluent was found to exhibit stronger reduction behaviour at cathodic bias potential but slightly less photoresponse at anodic bias than mixed dye.