The three-dimensional graphene microspheres with well-defined shape and size were prepared successfully by a novel approach, i.e., a combination of microfluidic device and freeze-drying. In the synthetic process, a pragmatic and facile device has been designed for the controllable generation of uniform-sized droplets. Followed by freeze-drying, highly porous spherical graphene microballs were obtained for further research. It is worth noting that the size of the droplets can also be controlled by adjusting the flow rate ratio of each phase. Afterward, the morphology, structure and character of the three-dimensional graphene particles are characterized by scanning electron microscope, X-ray diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Due to their highly porous structure, the as-prepared 3D graphene microspheres were employed as adsorbent. The adsorption capacity of acid orange 7 and Pb(II) was about 71.9 and 147.7 mg g−1, respectively. The results showed that the porous 3D graphene microspheres as adsorbent possessed excellent adsorption ability for organic and inorganic contaminants in this work, showing their potential applications in environmental pollutant treatment.

Self-propelled metal–organic framework (MOF)-based Janus micromotors that propel autonomously in hydrogen peroxide and display effective remediation of contaminated water is presented in this work. The novel Janus micromotors rely on the asymmetric deposition of a catalytically active Ag patch on the surface of MOF composite microspheres. The active Ag sites are used for the splitting of H2O2 to form oxygen bubbles. As a result, these Janus micromotors can reach a high speed of over 310 μm s−1 due to effective bubble propulsion, which is comparable to common Pt-based micromotors. By coupling the high catalytic capacity of MOFs with their autonomous propulsion, the MOF-based micromotors are shown to play a dominant role in the effective removal of organic pollutants. In addition, scanning electronic microscopy, Fourier-transform infrared spectroscopy and energy dispersive X-ray spectroscopy are performed to verify their morphology and composition. Based on the obtained results, a potential mechanism of the motion and the high catalytic activity is also proposed. It is expected that these energy saving micromotors with catalytic activity should be unprecedentedly spread in real applications.

•Combined effect of ultrasound and ZVAl on wastewater treatment was explored.•About 96% of AO7 can be degraded within 30 min under optimized conditions.•Effects of operating parameters on the degradation of AO7 were examined.Degradation of azo dye Acid Orange 7 (AO7) by zero-valent aluminum (ZVAl) in combination with ultrasonic irradiation was investigated. The preliminary studies of optimal degradation methodology were conducted with sole ultrasonic, sole ZVAl/air system, ultrasonication + ZVAl/air system (US-ZVAl). In ZVAl/air system, the degradation of AO7 could almost not be observed within 30 min. The degradation of AO7 by ZVAl/air system was obviously enhanced under ultrasound irradiation, and the enhancement is mainly attributed to that the production of hydroxyl radicals in ultrasound-ZVAl process was much higher than that in sole ultrasonic or in sole ZVAl/air system. The variables considered for the effect of degradation were the power of ultrasound, the initial concentration of AO7, as well as the initial pH value and the dosage of zero-valent aluminum. The results showed that the decolorization rate increased with the increase of power density and the dosage of ZVAl, but decreased with the increase of initial pH value and initial concentration of AO7. More than 96% of AO7 removal was achieved within 30 min under optimum operational conditions (AO7: 20 mg/L, ZVAl: 2 g/L, pH: 2.5, ultrasound: 20 kHz, 300 W). This study demonstrates that ultrasound-ZVAl process can effectively decolorize the azo dye AO7 in wastewater.

•APFO was effectively decomposed in persulfate/ultrasound system.•APFO decomposition under different conditions was studied.•The SO4−•/APFO reactions primarily occur at the bubble–water interface.Ammonium perfluorooctanoate (APFO) is an emerging environmental pollutant attracting significant attention due to its global distribution, high persistence, and bioaccumulation properties. The decomposition of APFO in aqueous solution with a combination of persulfate oxidant and ultrasonic irradiation was investigated. The effects of operating parameters, such as ultrasonic power, persulfate concentration, APFO concentration, and initial media pH on APFO degradation were discussed. In the absence of persulfate, 35.5% of initial APFO in 46.4 μmol/L solution under ultrasound irradiation, was decomposed rapidly after 120 min with the defluorination ratio reaching 6.73%. In contrast, when 10 mmol/L persulfate was used, 51.2% of initial APFO (46.4 μmol/L) was decomposed and the defluorination ratio reached 11.15% within 120 min reaction time. Enhancement of the decomposition of APFO can be explained by acceleration of substrate decarboxylation, induced by sulfate radical anions formed from the persulfate during ultrasonic irradiation. The SO4−•/APFO reactions at the bubble-water interface appear to be the primary pathway for the sonochemical degradation of the perfluorinated surfactants.

In this study, the polyhydroquinone/Fe3O4 (PHQ/Fe3O4) was synthesized as a heterogeneous catalyst to activate persulfate to effectively degrade Rhodamine B (RhB). The synthetic PHQ/Fe3O4 nanoparticles were characterized using X-ray diffraction (XRD), transmission electron microscope (TEM), Brunauer–Emmett–Teller (BET) nitrogen adsorption, and Fourier-transform infrared (FTIR) spectra. PHQ/Fe3O4 shows better catalytic performance and excellent reusability than PHQ and Fe3O4. The results indicated that PHQ/Fe3O4 maintains quinone units and the presence of the quinone moieties successfully accelerates the degradation compared to Fe3O4, owing to the role of quinone assisting the redox cycling of Fe. Effects of PHQ/Fe3O4 addition, persulfate concentration, pH, and temperature on the degradation efficiency of RhB by persulfate are examined in batch experiments. Increasing the temperature may significantly accelerate the RhB degradation, and the degradation is found to follow the pseudo-first-order kinetic model. On the basis of these findings, the possible mechanism of RhB degradation was proposed.

Degradation of the antibiotics amoxicillin in aqueous solution using sulphate radicals under ultrasound irradiation was investigated. The preliminary studies of optimal degradation methodology were conducted with only oxone (2KHSO5·KHSO4·K2SO4), cobalt activated oxone (oxone/Co2+), oxone + ultrasonication (oxone/US) and cobalt activated oxone + ultrasonication (oxone/Co2+/US). The chemical oxygen demand (COD) removal efficiency were in the order of oxone < oxone/Co2+ < oxone/US < oxone/Co2+/US for the amoxicillin solution. The variables considered for the effect of degradation were the temperature, the power of ultrasound, the concentration of oxone, as well as catalyst and the initial amoxicillin concentration. More than 98% of COD removal was achieved within 60 min under optimum operational conditions. Comparative analysis revealed that the sulfate radicals had the high oxidation potential and the use of ultrasound irradiation reduced the energy barrier of the reaction and increased the COD removal efficiency of organic pollutants. The degradation of amoxicillin follows the first-order kinetics.Highlights► Degradation of amoxicillin using sulphate radicals under ultrasound irradiation. ► Effect of operating parameters on the destruction of amoxicillin was examined. ► Synergistic effect of ultrasound on amoxicillin degradation with sulfate radical.

Sonochemical degradation of levofloxacin was investigated to assess the operational parameters and the impacts of rate enhancers (CCl4) and rate inhibitors (t-butanol). Different dosages of CCl4, pH value of solutions, ultrasonic power, and initial concentration of levofloxacin which affected the degradation of levofloxacin were studied. The degradation rate of levofloxacin was accelerated with increased concentrations of CCl4 via the accumulation of reactive chlorine species and the hindrance of OH radical combination reactions with atomic hydrogen. The addition of t-butanol at all test concentrations inhibited the degradation of levofloxacin regardless of the quantity of OH radicals in solution. It was also found that 5-day biochemical oxygen demand (BOD5) of the solution increased evidently after sonochemical treatment, and the ratio of BOD5/COD that was a good measure for biodegradability increased from 0 to 0.41, which indicated that biodegradability of the solution was obviously enhanced. Based on the results, it is feasible that sonochemical oxidation can be used for pretreatment of levofloxacin effluent before biological treatment processes.

•AQS-NH-MIL-101(Fe) composites were fabricated via a mild chemical method.•Immobilization of AQS on NH2-MIL-101(Fe) remarkably enhances BPA degradation.•Structural evolution and synergistic catalytic mechanisms were investigated.A novel quinone-modified metal-organic frameworks NH2-MIL-101(Fe) was synthesized using a simple chemical method under mild condition. The introduced 2-anthraquinone sulfonate (AQS) can be covalently modified with NH2-MIL-101(Fe) and acts as a redox mediator to enhance the degradation of bisphenol A (BPA) via persulfate activation. The obtained AQS-NH-MIL-101(Fe) was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectra, cyclic voltammetry and electrochemical impedance spectroscopy. AQS-NH-MIL-101(Fe) exhibited better catalytic performance compared with NH2-MIL-101(Fe) and NH2-MIL-101(Fe) with free AQS (NH2-MIL-101(Fe)/AQS). That is, AQS-NH-MIL-101(Fe) was proved to be the most effective in that more than 97.7% of BPA was removed. The degradation rate constants (k) of AQS-NH-MIL-101(Fe) was 9-fold higher than that of NH2-MIL-101(Fe) and 7-fold higher than NH2-MIL-101(Fe)/AQS, indicating that AQS is a great electron-transfer mediator when modified with NH2-MIL-101(Fe). Based on the above results, the possible mechanism of catalytic reaction has been investigated in view of the trapping experiments. In addition, the AQS-NH-MIL-101(Fe) catalyst exhibited excellent stability and can be used several times without significant deterioration in performance.Download full-size image