RESUMO
The efficiency of electrochemical nitrate (NO3-) reduction to ammonia (NH3) still remains a challenge due to the sluggish kinetics of the complex eight-electron reduction process and competitive hydrogen evolution reaction (HER). Herein, we designed new three-dimensional (3D) porous Cu/Cu2+1O nanosheet arrays (Cu/Cu2+1O NSA) by coupling a template-directed method with in situ electroreduction. Thanks to the 3D porous structure and in-plane heterojunctions, Cu/Cu2+1O NSA can provide abundant active sites and a good interfacial effect, obtaining the maximum Faradaic efficiency (FE) of ammonia (88.09%) and high yield rate of 0.2634 mmol h-1 cm-2, which is higher than that of CuO nanosheets (77.81% and 0.2188 mmol h-1 cm-2) and CuO nanoparticles (34.60% and 0.0692 mmol h-1 cm-2). Experimental results and DFT simulations show that the interface effect of Cu/Cu2+1O can decrease the reaction energy barrier of the key step (*NO to *NOH) and can greatly inhibit the competitive hydrogen evolution reaction, thereby achieving excellent electrocatalytic performance for nitrate-to-ammonia conversion.
RESUMO
Potocatalytic hydrogen evolution represnets a promising way to achieve renewable energy sources. Dual heterojunctions with an inverse opal structure are proposed for addressing fundamental challenges (low surface area, inefficient light absorption, and poor charge separation) in photocatalytic water splitting. Inverse opal structure and Co3O4 were introduced to design and synthesize a ZnO/ZnS/Co3O4 (IO-ZnO/ZnS/Co3O4) photocatalyst. Morphology characterizations and photoelectric measurements reveal that the introduction of three-dimensional (3D) structures and dual heterojunctions improves light utilization efficiency and accelerates charge separation, greatly promoting photoelectric performance. The as-prepared IO-ZnO/ZnS/Co3O4 manifests superior photocurrent density (0.49 mA/cm2), which is 4 times higher than that of IO-ZnO/ZnS due to the existence of dual heterojunctions. The result is further confirmed by an enhanced H2 production rate (153.01 µmol/g/h) in pure water. Notably, excellent cycling stability is achieved in pure water because Co3O4 can rapidly capture photogenerated holes to inhibit severe photocorrosion of ZnO/ZnS. Therefore, this work presents a new insight into inhibiting photocorrosion of metal sulfides and promoting their photoelectric performance by combining 3D structures and dual heterojunctions.
RESUMO
Searching for a new approach in environmental remediation in terms of dye degradation is important in industrialized society. In this work, ferroelectric Ba2.5Sr2.5Nb8Ta2O30 (BSNT) submicron powders prepared by the high-temperature solid-phase method are used for dye degradation under magnetic stirring. The dye in solution can be quickly degraded by magnetically stirring BSNT submicron particles in the dark in ambient temperature conditions. More importantly, the degradation efficiency can be greatly improved through simple modification of the stirring materials from glass to polypropylene, with a degradation efficiency of rhodamine B as high as 99% in 1.5 h at a gentle stirring speed of 300 rpm. Control experiments reveal that the degradation of the dye is mainly contributed by the friction between BSNT submicron particles and PTFE stirring rods. It is proposed that the friction between ferroelectric polar BSNT particles and PTFE causes charge transfer and induces a non-zero internal electric field to drive the separation of electron-hole pairs in BSNT particles, resulting in a novel tribocatalytic degradation of the dye, which is proven by the detection of ËOH and ËO2 - intermediate products during stirring. This work demonstrates that the friction energy of ferroelectric materials with strong polarization is an alternative approach for highly efficient dye degradation.