Mitigation of caffeine micropollutants in wastewater through Ag-doped ZnO photocatalyst: mechanism and environmental impacts.

Micropollutants, such as caffeine (M-CF), pose a significant threat to ecosystems and human health through water and food sources. The utilization of metal oxide-based photocatalysts has proven to be an effective treatment method for the removal of organic pollutants. This study explores the efficacy of Ag-doped ZnO (Ag/ZnO) for removing M-CF from wastewater. The characterization of Ag/ZnO underscores the crucial role of band gap energy in the photocatalytic degradation process. This parameter influences the separation of electrons and holes (e-/h+) and the generation of reactive radicals. Under solar light, Ag/ZnO demonstrated markedly superior photocatalytic activity, achieving an impressive degradation efficiency of approximately 93.4%, in stark contrast to the 53.2% occurred by ZnO. Moreover, Ag/ZnO exhibited a remarkable degradation efficiency of M-CF in wastewater, reaching 83.5%. A key advantage of Ag/ZnO lies in its potential for recovery and reuse in subsequent treatments, contributing to a reduction in operational costs for industrial wastewater treatment. Impressively, even after five cycles, Ag/ZnO maintained a noteworthy photodegradation rate of M-CF at 78.6%. These results strongly suggest that Ag/ZnO presents a promising solution for the removal of micropollutants in wastewater, with potential scalability for industrial and large-scale applications.

Improved Cr (VI) adsorption performance in wastewater and groundwater by synthesized magnetic adsorbent derived from Fe3O4 loaded corn straw biochar.

This work developed an easy method to utilize corn straw (CS) waste for sustainable development and reduce the volume of waste volume as well as bring value-added. The magnetic adsorbent was prepared by loading Fe3O4 onto biochar derived from corn straw (Fe@CSBC), then used for capturing Cr (VI) in groundwater and wastewater samples. The characterization of adsorbents showed that Fe3O4 was successfully loaded on corn straw biochar (CSBC) and contributed to the improvement of the surface area, and surface functional groups like Fe-O, Fe-OOH, CO, and O-H. The presence of iron oxide was further confirmed by XPS and XRD analysis and a magnetization value of 35.6 emu/g was obtained for Fe@CSBC. The highest uptake capacity of Cr (VI) onto Fe@CSBC and CSBC by monolayer were 138.8 and 90.6 mg/g, respectively. By applying magnetic adsorbent Fe@CSBC for the treatment of groundwater and wastewater samples, the chromium could be removed up to 90.3 and 72.6%, respectively. The remaining efficiency of Cr (VI) was found to be 84.5% after four times reused Fe@CSBC, demonstrating the great recyclable ability of the adsorbent. In addition, several interactions between Cr (VI) and Fe@CSBC like ion exchange, complexation, and reduction reaction were discussed in the proposed adsorption mechanism. This study brings an efficient method to turn corn straw biomass into an effective magnetic adsorbent with high adsorption performance and good reusability of Cr (VI) in groundwater as well as in wastewater.

Photodegradation of hazardous organic pollutants using titanium oxides -based photocatalytic: A review.

Titanium oxide-based photocatalysts (TOBPs) have been widely utilized as potential materials for numerous applications, such as wastewater treatment, water-splitting reactions, carbon dioxide (CO2) reduction and photosynthesis. However, the large bandgap of intrinsic TiO2 limits their absorption toward visible light, which is the central part of the solar spectrum, resulting in low photocatalytic activities under sunlight. To overcome this obstacle, several strategies, such as doping with either metal or non-metal elements or combining with other compounds, are efficient ways to reduce the bandgap of TiO2, leading to effectively extending their absorption toward the visible region and increasing their catalytic performance. In this review, we discussed the application of TOBPs for the photodegradation of hazardous organic pollutants in wastewater to produce quality reused water. The synthesis of TiO2 and the enhancement of photocatalytic activities of TOBPs by different techniques with detailed information were provided. Application of TOBPs for decomposing hazardous organic pollutants such as dyes, phenolic compounds and pharmaceuticals under optimum conditions have been listed. Also, the photodegradation mechanisms of hazardous organic compounds have been investigated. This work also brings ideas for future perspectives and research plan to inhibit the disadvantages and expand the application of TOBPs to remove toxic organic pollutants.

Adsorption and photodegradation of micropollutant in wastewater by photocatalyst TiO2/rice husk biochar.

With the acceleration of global industrialization, organic pollutants have become a threat to ecological safety and human health. This work prepared TiO2/rice husk biochar (TiO2/BC) for removal of bisphenol A (BA) micropollutant in wastewater. Experiment results revealed a low BA removal efficiency by TiO2/BC was observed at 34.5% under the dark environment. However, the removal rate of BA by UV light-assisted TiO2/BC significantly increased to 97.6% in 1 h. The results also demonstrated that the removal performance of BA using TiO2/BC was 2.1times higher than that of commercial TiO2 (46.4%). Besides, the removal efficiency of BA by reused TiO2/BC after eight cycles slightly decreased by 12.8%, demonstrating the excellent properties of the prepared composite. TiO2/BC also exhibited high removal efficiency of BA (over 89%) from the synthetic wastewater sample, indicating the potential utilization of composite for removing BA in wastewater. This work provides a new way to turn biomass waste into useful material and effective method to remove micropollutant BA.

Enhanced photodegradation of tetracycline in wastewater and conversion of CO2 by solar light assisted ZnO/g-C3N4.

Synthesized graphitic carbon nitride-based (CN) heterojunction photocatalysts are considered as a promising material for photodegradation of organic compounds and CO2 conversion. In this work, ZnO-loaded g-C3N4 (ZnO/CN) heterojunction photocatalyst was investigated for the enhanced photooxidation of tetracycline (TC) and CO2 conversion . After modification, the photocatalysts showed an improvement in the light absorption range and the photogenerated separation rate of electron/hole due to the heterojunction structure of ZnO/CN. The degradation rate of TC was found to be 92.6% within 60 min, while CO production rate was 7.68 µmol/g/h. The rate constants of TC by using ZnO/CN were 0.0812, 0.0539, 0.0336, 0.0249, and 0.0185 min-1, corresponding to the TC level of 1, 10, 30, 50, and 100 mg/L, respectively. The photodegradation rate of TC by ZnO/CN was 5 times higher than that of CN, demonstrating the advantage of heterojunction photocatalyst. The modified ZnO/CN exhibited superior degradation performance of TC and higher CO2 conversion rate than those of unmodified CN. It also exhibited high stability with 82% removal efficiency of TC at the 6th run and the CO2 conversion rate of 71% after reused 5 times. The heterojunction ZnO/CN can be utilized as an efficient material for various photocatalytic applications.

Magnesium oxide nanoparticles modified biochar derived from tea wastes for enhanced adsorption of o-chlorophenol from industrial wastewater.

In this work, magnesium oxide nanoparticles supported biochar derived from tea wastes (MgO@TBC) was prepared as an effective adsorbent for removing hazardous o-chlorophenol (o-CP) from industrial wastewater. The surface area, porous structure, surface functional groups and surface charge of tea waste biochar (TBC) significantly enhanced after the modification process. The best uptake performance of o-CP was found at pH = 6.5 and 0.1 g of MgO@TBC adsorbent. According to the adsorption isotherm, the adsorption of o-CP onto MgO@TBC followed the Langmuir model with a maximum uptake capacity of 128.7 mg/g, which was 26.5% higher than TBC (94.6 mg/g). MgO@TBC could be reused for eight cycles with a high o-CP uptake performance (over 60%). Besides, it also exhibited good removal performance of o-CP from industrial wastewater with a removal rate of 81.7%. The adsorption behaviors of o-CP onto MgO@TBC are discussed based on the experimental results. This work may provide information to prepare an effective adsorbent for removing hazardous organic contaminants in wastewater.

Alginate-modified biochar derived from rice husk waste for improvement uptake performance of lead in wastewater.

In this work, alginate-modified biochar derived from rice husk waste was synthesized using a simple process. The modified biochar (MBC) and rice husk biochar (RhBC) were investigated for removing Pb (II) ions in wastewater. The BET result displayed significantly improved specific surface area of MBC up to 120 m2/g along with a total pore volume of 0.653 cm3/g. FTIR spectrums presented the higher oxygen-contained functional groups of MBC as compared to RhBC, resulting in increasing adsorption capacity of Pb (II). MBC had higher adsorption capacity (112.3 mg/g) and faster removal rate (0.0081 g mg-1 min-1) than those of RhBC (41.2 mg/g and 0.00025 g mg-1 min-1). Modified RhBC can remove more than 99% of Pb (II) from wastewater and it could be utilized for three cycles with a removal performance of over 90%. In addition, the Pb adsorption mechanism by using MBC was proposed and the practical application of MBC for the treatment of wastewater in Vietnam was discussed.

Voltammetric Determination of Amoxicillin Using a Reduced Graphite Oxide Nanosheet Electrode.

A reduced graphite oxide nanosheet electrode (RGOnS) was prepared as a sensor for amoxicillin (AMX) detection, an antibiotic commonly used in the livestock farm, by the square-wave adsorptive stripping voltammetry technique. Graphite oxide with nanosheet shape was produced from a graphite electrode by a chronoamperometry process at 5 V and then an electrochemical reduction process was carried out to form RGOnS with restored long-range conjugated networks and better conductivity. The electrodes were characterized by SEM, EDX, and FTIR spectroscopy. The RGOnS electrode prepared at an optimal reduction potential of -1 V for 120 s exhibits a larger electrochemical active surface area, and the obtained oxidation signal of AMX is approximately ten times higher than that of the pristine graphite electrode. The analytical conditions such as the pH of electrolyte and accumulation time were optimized. The calibration curve built under the optimal conditions provided a good linear relationship in the range of AMX concentration from 0.5-80 µM with the correlation coefficient of 0.9992. The limit of detection was calculated as 0.193 µM. Satisfactory results are obtained from the detection of the AMX in different samples using the prepared electrode.