Hydrogen Production via Electrolysis of Wastewater.

The high energy consumption of traditional water splitting to produce hydrogen is mainly due to complex oxygen evolution reaction (OER), where low-economic-value O2 gas is generated. Meanwhile, cogeneration of H2 and O2 may result in the formation of an explosive H2/O2 gas mixture due to gas crossover. Considering these factors, a favorable anodic oxidation reaction is employed to replace OER, which not only reduces the voltage for H2 production at the cathode and avoids H2/O2 gas mixture but also generates value-added products at the anode. In recent years, this innovative strategy that combines anodic oxidation for H2 production has received intensive attention in the field of electrocatalysis. In this review, the latest research progress of a coupled hydrogen production system with pollutant degradation/upgrading is systematically introduced. Firstly, wastewater purification via anodic reaction, which produces free radicals instead of OER for pollutant degradation, is systematically presented. Then, the coupled system that allows for pollutant refining into high-value-added products combined with hydrogen production is displayed. Thirdly, the photoelectrical system for pollutant degradation and upgrade are briefly introduced. Finally, this review also discusses the challenges and future perspectives of this coupled system.

Pharmaceutical pollution fingerprinting and waterbodies remediation using waste-derived carbon dots as sustainable advanced nanomaterials.

The conversion of biomass waste into high-value nanomaterials such as carbon dots might represent a great advancement towards a circular economy system. Biomass wastes are an excellent choice as carbon precursors because of their wide availability, abundance, chemical composition, and eco-friendly nature. Moreover, their use as a raw material might decrease the total cost of the synthesis processes and reduce the environmental impacts. In addition, the complex composition of biomass leads to carbon dots with abundant functional groups, which in turn enhances water dispersibility and photoluminescence properties. In this manner, the effective transformation of biomass wastes into carbon dots reduces environmental pollution through the inadequate management of waste while producing carbon dots with enhanced performances. Therefore, this review describes biomass wastes as potential candidates for the synthesis of carbon dots through different synthesis methods. In addition, we have analyzed the great potential of biomass-derived carbon dots (CDs) for the degradation and detection of emerging pharmaceutical pollutants by promoting a circular economy approach. Finally, we identified current challenges to propose possible research directions for the large-scale and sustainable synthesis of high-quality biomass-derived CDs.

Rational design of CdS/BiOCl S-scheme heterojunction for effective boosting piezocatalytic H2 evolution and pollutants degradation performances.

Piezocatalysis as an emerging technology is broadly applied in hydrogen evolution and organic pollutants degradation aspects. However, the dissatisfactory piezocatalytic activity is a severe bottleneck for its practical applications. In this work, CdS/BiOCl S-scheme heterojunction piezocatalysts were constructed and explored the performances of piezocatalytic hydrogen (H2) evolution and organic pollutants degradation (methylene orange, rhodamine B and tetracycline hydrochloride) under strain by ultrasonic vibration. Interestingly, CdS/BiOCl presents a volcano-type relationship between catalytic activity and CdS contents, namely firstly increases and then decreases with the increase of CdS content. Optimal 20 % CdS/BiOCl endows superior piezocatalytic H2 generation rate of 1048.2 µmol g-1h-1 in methanol solution, which is 2.3 and 3.4 times higher than that of pure BiOCl and CdS, respectively. This value is also much higher than the recently reported Bi-based and most of other typical piezocatalysts. Meanwhile, 5 % CdS/BiOCl delivers the highest reaction kinetics rate constant and degradation rate toward various pollutants compared with other catalysts, which also exceeds that of the previously numerous results. Improved catalytic capacity of CdS/BiOCl is mainly ascribed to the construction of S-scheme heterojunction for enhancing the redox capacity as well as inducing more effective charge carriers separation and transfer. Moreover, S-scheme charge transfer mechanism is demonstrated via electron paramagnetic resonance and Quasi-In-situ X-ray photoelectron spectroscopy measurements. Eventually, a novel piezocatalytic mechanism of CdS/BiOCl S-scheme heterojunction has been proposed. This research develops a novel pathway for designing highly efficient piezocatalysts and provides a deeper understanding in construction of Bi-based S-scheme heterojunction catalysts for energy conservation and wastewater disposal applications.

Dual-stimuli-responsive CuS-based micromotors for efficient photo-Fenton degradation of antibiotics.

Antibiotics as emerging pollutants in water pose great risks to human health. Due to their persistence in the environment, advanced oxidation processes (AOPs) have been proposed for the degradation of antibiotics. Therefore, developing efficient catalysts for AOPs becomes critical for the removal of antibiotics. Herein, we develop self-propelled CuS-based micromotors (CuS@Fe3O4/Pt) as active heterogenous catalysts for efficient photo-Fenton degradation of antibiotics. Combining the merits of conventional heterogenous and homogenous catalysts, the prepared micromotors are easy to recycle and free of secondary pollution risks, while demonstrating high degradation efficiency due to self-induced intensification of mass transfer via autonomous motion and microbubble generation. The H2O2 in the Fenton reagents can serve as the fuel for the micromotors to drive their self-propulsion by bubbles generated from catalytic decomposition of H2O2 by the platinum layer. The dual-stimuli-responsiveness of the micromotors to magnetic field and light irradiation allows multi-modes of propulsion and guidance in different systems. The efficient photothermal effect of CuS enables the micromotors to achieve collective phototactic motion toward light, whereas magnetic responsiveness facilitates the recovery and collection of the micromotors. The synergistic effect of CuS and Fe3O4 NPs in H2O2 under visible light irradiation generates a large amount of OH· and ·O2- to effectively degrade tetracycline within several minutes. With these advantages, the dual-stimuli-responsive CuS-based micromotors provide a new strategy for enhanced degradation of antibiotics in water purification applications.

Transition Metal and Metal-Nx Codoped MOF-Derived Fenton-Like Catalysts: A Comparative Study on Single Atoms and Nanoparticles.

To deal with the ever-growing toxic benzene-derived compounds in the water system, extensive efforts have been dedicated for catalytic degradation of pollutants. However, the activities and efficiencies of the transition metal-based nanoparticles or single-atom sites are still ambiguous in Fenton-like reactions. Herein, to compare the Fenton-like catalytic efficiencies of the nanoparticles and single atoms, the free-standing nanofibrous catalyst comprising Co nanocrystals and Co-Nx codoped carbon nanotubes (CNTs) or bare Co-Nx doped CNTs is fabricated. It is noteworthy that all these nanofibrous catalysts exhibit efficient activities, mesoporous structures, and conductive carbon networks, which allow a feasible validation of the catalytic effects. Benefiting from the maximized atomic utilization, the atomic Co-Nx centers exhibit much higher reaction kinetic constant (κ = 0.157 min-1 ) and mass activity toward the degradation of bisphenol A, far exceeding the Co nanocrystals (κ = 0.082 min-1 ). However, for the volume activities, the single-atom catalyst does not show apparent advantages compared to the nanocrystal-based catalyst. Overall, this work not only provides a viable pathway for comparing Fenton-like catalytic effects of transition metal-based nanoparticles or single atoms but also opens up a new avenue for developing prominent catalysts for organic pollutants' degradation.

Construction of novel Pd/CeO2/g-C3N4 nanocomposites as efficient visible-light photocatalysts for hexavalent chromium detoxification.

In this study, we report a series of novel palladium nanoparticles (Pd) supported cerium oxide (CeO2)/graphitic carbon nitride (g-C3N4) nanocomposites, fabricated via the simple strategy, which were used for the detoxification of toxic hexavalent chromium to benign trivalent chromium under visible light irradiation. The synthesized Pd/CeO2/g-C3N4 nanocomposites were characterized by various tools including powder X-ray diffraction (PXRD), fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectra (DRS/UV-vis), high resolution transmission electron microscopy (HRTEM), and energy dispersive X-ray spectra (EDS). The wrapping with surface of graphitic carbon nitride nanosheets can efficiently promote the interface charge separation and transmission over the ternary photocatalyst, which was studied by photoluminescence spectra (PL) analysis and electrochemical impedance spectroscopy (EIS) spectra. The obtained 3% Pd/CeO2/g-C3N4 nanocomposite photocatalyst exhibit an excellent photocatalytic performance when compared to other single and composite counter parts. The 3% Pd/CeO2/g-C3N4 exhibits a strong synergistic effect which arises due to the interactions between palladium nanoparticles, CeO2 and graphitic carbon nitride resulting in the lower recombination of photo-induced charge carriers with enhanced photocatalytic activity. This work implies that the synergistic Pd/CeO2/g-C3N4 nanocomposites would be a new kind of high-efficiency visible-light-driven photocatalysts materials for the detoxification of public safety and security.

Nanocristales para degradación de un colorante contaminante / Nanocrystals for the degradation of a pollutant dye / Nanocristais para a degradação de um corante poluente

La fotoestabilidad de nanocristales (NCs) del grupo E-VI, como CdSe se aprovecha en procesos de fotocatálisis. Sin embargo, el contenido de metales tóxicos limita su aplicación en el ambiente en la remediación de residuos de las industrias textiles, de pieles y de papel. Se comparó la acción catalítica de CdS y ZnS, estabilizadas con dodecil sulfato de sodio y ácido etilendiaminotetraacético, respectivamente, para el tratamiento fotocatalítico del colorante azul de metileno (AM) con radiación UV. Las dos clases de NCs presentaron bandas de absorción desplazadas hacia 500 nm y bandas de emisión fluorescente a 430-440 nm. Estas características ópticas se atribuyen al tamaño (20-50 y 100-150 nm), confirmado por microscopía electrónica. La degradación del AM por NCs alcanzó rendimientos del 92% y 77% para ZnS y CdS respectivamente, mediante la producción fotocatalítica de radicales hidroxilos capaces de participar en procesos redox. En conclusión, NCs se aprecian como catalizadores eficientes para la remediación de AM, un colorante aromático heterocíclico de amplio uso industrial.

The photo-stability of nanocrystals (NCs) in II-VI group such as CdSe is used for photo-catalytic processes. The presence of toxic metals limits their implementation in environmental applications such as synthetic dyes treatment, which are found in textile, leather, and paper industries. NCs ZnS and CdS, stabilized in the presence of ethylendiaminetetraacetic acid and sodium dodecyl sulfate, respectively, were compared in the photo-catalytic treatment of methylene blue (MB), under UV light. The two kinds of NCs showed absorption bands displaced towards 500 nm and fluorescent emission bands around 430 nm. These optical properties are attributed to nano size as observed by scanning electron microscopy (20-50 and 100-150 nm). MB degradation by NCs reached yields up to 92% and 77% for ZnS and CdS, respectively, due to the photo-catalytic production of hydroxyl radicals capable of participating in redox processes. In conclusion, NCs catalyzed the remediation of MB, a heterocyclic aromatic dye of broad industrial use.

A fotoestabilidade do nanomateriais (NCs) do grupo II-VI como CdSe é usada em processos de fotocatálise. Mas a presença de metais tóxicos limita sua implementação no ambiente para remediar os residuos das industrias têxteis, de couro e de papel. Foi comparada a ação catalítica de ZnS e CdS, estabilizados na presenca de dodecil sulfato de sódio e ácido etilenodiamino tetra-acético, respectivamente, para o tratamento fotocatalítico de azul de metileno (AM) com radiação UV. Os dois tipos de NCs mostraram bandas de absorção perto de 500 nm e bandas de emissao fluorescente a 430-440 nm Estas propriedades ópticas são atribuídas ao tamanho (20-50 y 100-150 nm) confirmado por microscopia electrónica A degradação do AM por NCs alcancou rendimentos de 92% e 77% para ZnS e CdS respectivamente, através da produção fotocatalítica de radicais hidroxilo capazes de participar em processos redox Em conclusão NCs são vistos como catalisadores eficientes para a remediação de AM, um corante de amplia utilização industrial.

Physical and chemical effects of acoustic cavitation in selected ultrasonic cleaning applications.

Acoustic cavitation in a liquid medium generates several physical and chemical effects. The oscillation and collapse of cavitation bubbles, driven at low ultrasonic frequencies (e.g., 20 kHz), can generate strong shear forces, microjets, microstreaming and shockwaves. Such strong physical forces have been used in cleaning and flux improvement of ultrafiltration processes. These physical effects have also been shown to deactivate pathogens. The efficiency of deactivation of pathogens is not only dependent on ultrasonic experimental parameters, but also on the properties of the pathogens themselves. Bacteria with thick shell wall are found to be resistant to ultrasonic deactivation process. Some evidence does suggest that the chemical effects (radicals) of acoustic cavitation are also effective in deactivating pathogens. Another aspect of cleaning, namely, purification of water contaminated with organic and inorganic pollutants, has also been discussed in detail. Strong oxidising agents produced within acoustic cavitation bubbles could be used to degrade organic pollutants and convert toxic inorganic pollutants to less harmful substances. The effect of ultrasonic frequency and surface activity of solutes on the sonochemical degradation efficiency has also been discussed in this overview.

Efficient biocatalytic degradation of pollutants by enzyme-releasing self-propelled motors.

The first example of a self-propelled tubular motor that releases an enzyme for the efficient biocatalytic degradation of chemical pollutants is demonstrated. How the motors are self-propelled by the Marangoni effect, involving simultaneous release of SDS surfactant and the enzyme remediation agent (laccase) in the polluted sample, is illustrated. The movement induces fluid convection and leads to the rapid dispersion of laccase into the contaminated solution and to a dramatically accelerated biocatalytic decontamination process. The greatly improved degradation efficiency, compared to quiescent solutions containing excess levels of the free enzyme, is illustrated for the efficient biocatalytic degradation of phenolic and azo-type pollutants. The high efficiency of the motor-based decontamination approach makes it extremely attractive for a wide-range of remediation processes in the environmental, defense and public health fields.