Advanced degradation of organic pollutants using sonophotocatalytic peroxymonosulfate activation with CoFe2O4/Cu- and Ce-doped SnO2 composites

The rampant upsurge of organic pollutants in aqueous media has become one of the major concerns nowadays. Finding non-specific catalysts that can target a wide range of organic pollutants is a key challenge. Eco-friendly oxidative radicals, such as promoted by peroxymonosulfate (PMS), are necessary for efficient water decontamination. We propose a multicomponent composite catalyst for activating PMS using a dual strategy of sonophotocatalysis. The composite integrates cobalt ferrite and Cu- or Ce-doped SnO2, with the at. % of doping metal and the mixture ratio carefully balanced. The top-performing architectures were able to decompose rhodamine B (20 ppm), a representative pollutant, in under 3 min and achieve over 70% mineralization in just 5 min. The synthesized nanocomposites demonstrated exceptional sonophotocatalytic performance, even when treating complex and diverse multipollutant solutions (80 ppm), achieving over 75% mineralization after 150 min. Considering their high stability and reusability, the proposed CoFe2O4/Cu- and Ce-doped SnO2 materials are among the state-of-the-art heterogeneous catalysts for mineralizing organic pollutants through PMS activation

Visible-light driven sonophotocatalytic removal of tetracycline using Ca-doped ZnO nanoparticles

Highly efficient, long-term, eco-friendly catalysts for water decontamination technology are urgently needed to meet the prioritized objectives of green development and societies worldwide. Ca-doped ZnO were investigated as environmentally friendly sono-photocatalytic system under LED visible light irradiation to efficiently mineralize tetracycline-based antibiotics. The effects of pH, Ca doping, light, ultrasound, and pH on the mineralization of tetracycline by Ca-doped ZnO nanopowders and on the chemical, sono-, photo- and sono-photostability of Ca-doped ZnO nanopowders were systematically investigated. The ZnO-based catalyst with 2 at. % of Ca dopant exhibited the best sono-photocatalytic performance in mineralizing tetracyclines under visible LED light and ultrasound irradiation (i.e., 99% mineralization in 90 min), with excellent reusability and minimal sono-photocorrosion (i.e., 1% of catalyst dissolution in 180 min), which were even greater in the absence of organic pollutants and in the pH range of most natural waters. For Ca-doped ZnO nanopowders, the role of the generated reactive oxygen species under light and ultrasound stimulation and the mechanism of the mineralization of tetracycline were analyzed. In conclusion, the sono-photocatalytic mineralization of antibiotics synergizing visible LED light and weak ultrasound irradiation in the presence of Ca-doped ZnO nanopowders presents an outstanding start to developing highly efficient, long-term, eco-friendly catalysts for efficiently treating emerging organic pollutants

Synthesis, Characterization and Sensing Properties of AZO and IZO Nanomaterials

Al-doped ZnO (AZO) and In-doped ZnO (IZO) nanopowders were prepared by a sol-gel route and subsequent drying in ethanol under supercritical conditions. The morphological and microstructural properties were investigated by transmission electron microscopy (TEM) analysis and X-ray powder diffraction (XRD). The characterization study showed that the AZO and IZO nanoparticles were crystalline and exhibited the hexagonal wurtzite structure. Chemoresistive devices consisting of a thick layer of synthesized nanoparticles on interdigitated alumina substrates have been fabricated and their electrical and sensing characteristics were investigated. The sensor performances of the AZO and IZO nanoparticles for carbon monoxide (CO) were reported. The results indicated that both doped-sensors exhibited higher response and quick response/recovery dynamics compared to a ZnO-based sensor. These interesting sensing properties were discussed on the basis of the characterization data reported

CO and NO2 Selective Monitoring by ZnO-Based Sensors

ZnO nanomaterials with different shapes were synthesized, characterized and tested in the selective monitoring of low concentration of CO and NO2 in air. ZnO nanoparticles (NPs) and nanofibers (NFs) were synthesized by a modified sol-gel method in supercritical conditions and electrospinning technique, respectively. CO and NO2 sensing tests have demonstrated that the annealing temperature and shape of zinc oxide nanomaterials are the key factors in modulating the electrical and sensing properties. Specifically, ZnO NPs annealed at high temperature (700 °C) have been found sensitive to CO, while they displayed negligible response to NO2. The opposite behavior has been registered for the one-dimensional ZnO NFs annealed at medium temperature (400 °C). Due to their adaptable sensitivity/selectivity characteristics, the developed sensors show promising applications in dual air quality control systems for closed ambient such as automotive cabin, parking garage and tunnels

NO2 Selective Sensor Based on α-Fe2O3 Nanoparticles Synthesized via Hydrothermal Technique

In the present work, hematite (α-Fe2O3) nanopowders were successfully prepared via a hydrothermal route. The morphology and microstructure of the synthesized nanopowders were analyzed by using scanning and transmission electron microscopy (SEM and TEM, respectively) analysis and X-ray diffraction. Gas sensing devices were fabricated by printing α-Fe2O3 nanopowders on alumina substrates provided with an interdigitated platinum electrode. To determine the sensor sensitivity toward NO2, one of the main environmental pollutants, tests with low concentrations of NO2 in air were carried out. The results of sensing tests performed at the operating temperature of 200 °C have shown that the α-Fe2O3 sensor exhibits p-type semiconductor behavior and high sensitivity. Further, the dynamics exhibited by the sensor are also very fast. Lastly, to determine the selectivity of the α-Fe2O3 sensor, it was tested toward different gases. The sensor displayed large selectivity to nitrogen dioxide, which can be attributed to larger affinity towards NO2 in comparison to other pollutant gases present in the environment, such as CO and CO2

Synthesis, Characterization and Sensing Properties of AZO and IZO Nanomaterials

Al-doped ZnO (AZO) and In-doped ZnO (IZO) nanopowders were prepared by a sol-gel route and subsequent drying in ethanol under supercritical conditions. The morphological and microstructural properties were investigated by transmission electron microscopy (TEM) analysis and X-ray powder diffraction (XRD). The characterization study showed that the AZO and IZO nanoparticles were crystalline and exhibited the hexagonal wurtzite structure. Chemoresistive devices consisting of a thick layer of synthesized nanoparticles on interdigitated alumina substrates have been fabricated and their electrical and sensing characteristics were investigated. The sensor performances of the AZO and IZO nanoparticles for carbon monoxide (CO) were reported. The results indicated that both doped-sensors exhibited higher response and quick response/recovery dynamics compared to a ZnO-based sensor. These interesting sensing properties were discussed on the basis of the characterization data reported

CO and NO2 Selective Monitoring by ZnO-Based Sensors

ZnO nanomaterials with different shapes were synthesized, characterized and tested in the selective monitoring of low concentration of CO and NO2 in air. ZnO nanoparticles (NPs) and nanofibers (NFs) were synthesized by a modified sol-gel method in supercritical conditions and electrospinning technique, respectively. CO and NO2 sensing tests have demonstrated that the annealing temperature and shape of zinc oxide nanomaterials are the key factors in modulating the electrical and sensing properties. Specifically, ZnO NPs annealed at high temperature (700 °C) have been found sensitive to CO, while they displayed negligible response to NO2. The opposite behavior has been registered for the one-dimensional ZnO NFs annealed at medium temperature (400 °C). Due to their adaptable sensitivity/selectivity characteristics, the developed sensors show promising applications in dual air quality control systems for closed ambient such as automotive cabin, parking garage and tunnels

Co₃O₄/Al-ZnO Nano-composites: Gas Sensing Properties

In this paper, the gas sensing properties of metal oxide nano-powder composites are studied and modeled. The gas sensing properties of mixtures of two different metal oxide nanoparticles, prepared via low-cost routes, are investigated. The responses to both an oxidizing (NO2) and a reducing gas (CO) are analyzed. The tested composites are obtained by mixing a different percentage of a p-type metal oxide, Co3O4, with moderate responses to NO2 at about 200 °C and to CO at high temperature (above 260 °C), with n-type Al-doped ZnO, which is characterized by a large but unstable response towards NO2 around 160 °C and a moderate response towards CO around 200 °C. In the oxides mixtures, p-n heterojunctions are formed by the juxtaposition of an n-type and a p-type grain in contact. Consequently, the electronic conductivity is modified and the obtained composite materials show novel characteristics with respect to the base materials. This indicates that predicting the behavior of the composites from those of their components is not possible and it suggests that the hetero-junction behavior has to be studied to understand the sensing properties of the composite materials. The obtained results indicate that the composites containing a significant amount of hetero-junctions exhibit a stable response to NO2 at room temperature and significant responses towards CO at 160 °C

Nanostructured Nickel on Porous Carbon-Silica Matrix as an Efficient Electrocatalytic Material for a Non-Enzymatic Glucose Sensor

Nanostructured nickel on porous carbon-silica matrix (N-CS) has been synthesized using a sol gel process and subsequent pyrolysis treatment at a temperature of 650 °C. The morphology and microstructure of the N-CS sample has been investigated using XRD (X-ray Diffraction), SEM-EDS (Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy), and BET (Brunauer-Emmett-Teller) analysis. The synthesized nanocomposite has been used for developing NCS-modified screen-printed electrodes (NCS-SPCEs) and was applied in the electrochemical monitoring of glucose. After electrochemical activation, via cycling the modified electrode in a potential window from 0 to 0.8 V in 0.1 M KOH solution, the fabricated NCS-SPCEs electrodes were evaluated for the voltammetric and amperometric determination of glucose. The developed sensors showed good sensing performance towards glucose, displaying a sensitivity of 585 µA/mM cm−1 in the linear range from 0.05 to 1.5 mM, a detection limit lower than 30 µM with excellent selectivity