The removal of methylene blue as a remedy of dye-based marine pollution: a photocatalytic perspective

Efficient photocatalytic methylene blue dye degradation from green-synthesized silver-doped iron oxide (Ag@Fe2O3) nanostructures

This study presents an environmentally friendly method for synthesizing Ag@Fe2O3 nanostructures through a hydrothermal technique that utilizes Saussurea obvallata leaf extract as a reducing and capping agent. The material was characterized using UV-Vis, FTIR, XRD, SEM-EDX, and TEM-SAED-line profile analysis. The UV-Vis shows a maximum absorbance peak at 380 nm, showing a band gap of 3.26 eV. FTIR analysis revealed several functional groups (vibrational modes), including 944 and 514 cm-1 (Fe-O) and 445 cm-1 (Ag-O). XRD spectra analysis confirmed the crystalline nature and, using the Scherrer equation, showed an average crystallite size of 49.57 nm. EDX confirmed the presence of only Ag, Fe, and O elements. SEM and TEM-SAED analyses revealed an echinus-like morphology with an interplanar spacing of 126 pm of the nanostructures. The photocatalytic activity of Ag@Fe2O3 was investigated through the degradation of methylene blue (MB) dye in the presence of UV-visible light irradiation. It was observed that 97.10% MB dye degradation occurred within 60 min, with the rate constant and half-life being 0.03025 min-1 and 22.90 min, respectively. It was deduced that the synergistic interaction of Ag with Fe2O3 promoted the separation of charge, significantly diminishing electron-hole recombination. This research presents plant extract as a readily available, cost-effective, and environmentally friendly way to produce highly efficient photocatalysts for degrading wastewater dye compounds.

Removal of Methylene Blue Dye from Aqueous Solutions by Pullulan Polysaccharide/Polyacrylamide/Activated Carbon Complex Hydrogel Adsorption

In this study, composite hydrogels were prepared using a simple synthetic technique to adsorb methylene blue (MB) from water. The hydrogel comprised potassium persulfate (KPS) as the initiator, N,N'-methylene bisacrylamide as the crosslinking agent, and sodium hydroxide (NaOH) as the activator. It was employed to adsorb MB at different concentrations from water. The morphology and properties of PUL/PAM/GO composites were characterized through thermogravimetric analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy. Moreover, the adsorption properties, adsorption isotherms, adsorption kinetics, adsorption thermodynamics, and swelling properties of the hydrogel for MB were investigated. The optimal ratio of PUL to AC was obtained as 6:1 by fixing the amount of PUL and loading AC of different masses. The maximum adsorption capacity was obtained as 591.4 mg/g. It also exhibited certain mechanical strength. The adsorption of MB conforms to pseudo-first-order kinetics and Langmuir isotherms. In this study, an environment-friendly, cheap, simple, and efficient way was presented for the composite hydrogel in the direction of water treatment.

Application of visible light active photocatalysis for water contaminants: A review

Organic water pollutants are ubiquitous in the natural environment arising from domestic products as well as current and legacy industrial processes. Many of these organic water pollutants are recalcitrant and only partially degraded using conventional water and wastewater treatment processes. In recent decades, visible light active photocatalyst has gained attention as a non-conventional alternative for the removal of organic pollutants during water treatment, including industrial wastewater and drinking water treatment. This paper reviews the current state of research on the use of visible light active photocatalysts, their modified methods, efficacy, and pilot-scale applications for the degradation of organic pollutants in water supplies and waste streams. Initially, the general mechanism of the visible light active photocatalyst is evaluated, followed by an overview of the major synthesis techniques. Because few of these photocatalysts are commercialized, particular attention was given to summarizing the different types of visible light active photocatalysts developed to the pilot-scale stage for practical application and commercialization. The organic pollutant degradation ability of these visible light active photocatalysts was found to be considerable and in many cases comparable with existing and commercially available advanced oxidation processes. Finally, this review concludes with a summary of current achievements and challenges as well as possible directions for further research. PRACTITIONER POINTS: Visible light active photocatalysis is a promising advanced oxidation process (AOP) for the reduction of organic water pollutants. Various mechanisms of photocatalysis using visible light active materials are identified and discussed. Many recent photocatalysts are synthesized from renewable materials that are more sustainable for applications in the 21st century. Only a small number of pilot-scale applications exist and these are outlined in this review.

The Combined Effect of Bubble and Photo Catalysis Technology in BTEX Removal from Produced Water

Among the several ways used in wastewater treatment, the photocatalysis process is a more novel and alternative process that is increasingly employed in recent years. This work aims to improve the performance of the photocatalyst process by using air bubbles in removing the BTEX from produced water as an indicator of process efficiency. The study also shows the effect of influencing factors (pH and residence time) on the photocatalysis process. The study was done in a rectangular column with dimensions of 200 mm width, 30 mm depth, and 1500 mm height. Commercial titanium oxide (TiO2) coated on a plate by the varnish was used as a source of the photocatalyst. The experiment was carried out under different values of gas flow rate (0-3 L/min) to evaluate its effect on the photocatalyst process, the effect of other variables of pH (3-11), and irradiation time (30-120) min was also studied. A new method of the coating was adopted by using an alumina plate with varnish as an adhesive. The characteristics results show that the coated plate has hydrophilic properties and that there is no significant change in the crystal structure of the TiO2 nanoparticles and the varnish before and after 60 h of the photocatalytic process, indicating that the plate is still effective after 60 h usage under different conditions. The results also show that the introduction of air bubbles enhances the removal efficiency of BTEX significantly and the best removal effectiveness of BTEX was 93% when pH = 5 after 90 min and 90% when pH = 3 after 120 min. The removal rate also reached 86% when pH = 7 after 120 min all at a flow rate of 3 L/min. The percentage of removal decreased at pH = 9 and 11, reaching 64% and 50%, respectively after 120 min and a flow rate of 3 L/min. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).