Numerical and experimental investigations of liquid mixing in two-stage micro-impinging stream reactors

Controllable and Scale-Up Synthesis of Nickel-Cobalt Boride@Borate/RGO Nanoflakes via Reactive Impingement Mixing: A High-Performance Supercapacitor Electrode and Electrocatalyst

Large-scale synthesis of graphene-based nanomaterials in stirred tank reactor (STR) often results in serious agglomeration because of the poor control during micromixing process. In this work, reactive impingement mixing is conducted in a two-stage impinging jet microreactor (TS-IJMR) for the controllable and scale-up synthesis of nickel-cobalt boride@borate core-shell nanostructures on RGO flakes (NCBO/RGO). Benefiting from the good process control and improved micromixing efficiency of TS-IJMR, NCBO/RGO nanosheet provides a large BET surface area, abundant of suitable mesopores (2–5 nm), fast ion diffusion, and facile electron transfer within the whole electrode. Therefore, NCBO/RGO electrode exhibits a high specific capacitance of 2383 F g−1 at 1 A g−1, and still retains 1650 F g−1 when the current density is increased to 20 A g−1, much higher than those of nickel boride@borate/RGO (NBO/RGO) and cobalt boride@borate/RGO (CBO/RGO) synthesized in TS-IJMR, as well as NCBO/RGO-S synthesized in STR. In addition, an asymmetric supercapacitor (NCBO/RGO//AC) is constructed with NCBO/RGO and activated carbon (AC), which displays a high energy density of 53.3 W h kg−1 and long cyclic lifespan with 91.8% capacitance retention after 5000 charge-discharge cycles. Finally, NCBO/RGO is used as OER electrocatalyst to possess a low overpotential of 309 mV at a current density of 10 mA cm−2 and delivers a good long-term durability for 10 h. This study opens up the potential of controllable and scale-up synthesis of NCBO/RGO nanosheets for high-performance supercapacitor electrode materials and OER catalysts.

CFD modeling of a UV-A LED baffled flat-plate photoreactor for environment applications: a mining wastewater case

The use of ultraviolet light in photoreactors for wastewater treatment has become popular as an alternative of known chemical oxidative substances. UV LED light represents cheaper, robust, and versatile alternative to traditional UV lamps. In this study, it was designed and evaluated a photoreactor with an approach of chemical fluid dynamics (CFD) and experimental validation. The evaluation consisted of (1) CFD velocity profile analysis, (2) characterization of the average light distribution with potassium ferrioxalate actinometry, (3) degradation of a typical recalcitrant metallic cyanocomplex Fe(CN)₆^3-, and (4) scavenger effect analysis in the photodegradation using potassium persulfate. Actinometrical essay concluded that the system was able to receive 1.93 μE/s. The reactor operated under turbulent regime and best result for Fe(CN)₆^3- degradation was obtained at 4 h of operation, using 5-W UV-A LEDs, with pH ~ 7 and 10 mM de S₂O₈^2-. Baffled photoreactor demonstrated to be useful for this type of illumination and wastewater treatment.