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Bismuth vanadate (BiVO4) has been considered as a promising photoelectrocatalytic (PEC) semiconductor, but suffers from severe hole recombination, attributed to the short hole-diffusion length and the low carrier mobility. Herein, a type-II heterojunction CdIn2S4/BiVO4is designed to improve the photocurrent density from 1.22 (pristine BiVO4) to 2.68 mA cm–2at 1.23 V vs the reversible hydrogen electrode (RHE), accelerating the bulk separation of photogenerated carriers by the built-in field from the matched energy band. With the introduction of CQDs, CQDs/CdIn2S4/BiVO4increases the photocurrent density to 4.84 mA cm–2, enhancing the light absorption and cathodically shifting its onset potential, due to the synergetic effect of the heterojunction and CQDs. Compared with BiVO4, CQDs/CdIn2S4/BiVO4promotes the bulk separation efficiency to 94.6% and the surface injection efficiency to 72.2%. Additionally, spin-coating of FeOOH on CQDs/CdIn2S4/BiVO4could further improve the PEC performance and keep a long stability for water splitting. The density function theory (DFT) calculations illustrated that the type-II heterojunction CdIn2S4/BiVO4could decrease the oxygen evolution reaction (OER) overpotential and accelerate bulk charge separation for the built-in field of the aligned band structure.

Bismuth vanadate (BiVO4) as a fascinating semiconductor for photoelectrocatalytic (PEC) water oxidation with suitable band gap (Eg) has been limited by the issue of poor separation and transportation of charge carriers. Herein, we propose an unconventional substitution of V5+sites by Ti4+in BiVO4(Ti:BiVO4) for the similar ionic radii and accelerated polaron hopping. Ti:BiVO4increased the photocurrent density 1.90 times up to 2.51 mA cm–2at 1.23 V vs RHE and increased the charge carrier density 1.81 times to 5.86 × 1018cm–3. Compared with bare BiVO4, Ti:BiVO4improves the bulk separation efficiency to 88.3% at 1.23 V vs RHE. The DFT calculations have illustrated that Ti-doping modification could decrease the polaron hopping energy barrier, narrow the Eg, and decrease the overpotential of the oxygen evolution reaction (OER) concurrently. With further spin-coated FeOOH cocatalyst, the photoanode has a photocurrent density of 3.99 mA cm–2at 1.23 V vs RHE. The excellent PEC performance of FeOOH/Ti:BiVO4is attributed to the synergistic effect of the FeOOH layer and Ti doping, which could promote charge carrier separation and transfer by expediting polaron migration.

The conversion of excess ammonia N into harmless N2is a primary challenge for wastewater treatment. We present here a method to generate ClO•directionally for quick and efficient decomposition of NH4+N to N2. ClO•was produced and enhanced by a bifacial anode, a front WO3photoanode and a rear Sb–SnO2anode, in which HO•generated on WO3reacts with HClO generated on Sb–SnO2to form ClO•. Results show that the ammonia decomposition rate of Sb–SnO2/WO3is 4.4 times than that of WO3and 3.3 times than that of Sb–SnO2, with achievement of the removal of NH4+N on Sb–SnO2/WO3and WO3being 99.2 and 58.3% in 90 min, respectively. This enhancement is attributed to the high rate constant of ClO•with NH4+N, which is 2.8 and 34.8 times than those of Cl•and HO•, respectively. The steady-state concentration of ClO•(2.5 × 10–13M) is 102times those of HO•and Cl•, and this is further confirmed by kinetic simulations. In combination with the Pd–Cu/NF cathode to form a denitrification exhaustion system, Sb–SnO2/WO3shows excellent total nitrogen removal (98.4%), which is more effective than WO3(47.1%) in 90 min. This study provides new insight on the directed ClO•generation and its application on ammonia wastewater treatment.

A series of triple hierarchical micro-meso-macroporous N-doped carbon shells with hollow cores have been successfully prepared via etching N-doped hollow carbon spheres with CO2at high temperatures. The surface areas, total pore volumes and micropore percentages of the CO2-activated samples evidently increase with increasing activation temperature from 800 to 950 °C, while the N contents show a contrary trend from 7.6 to 3.8 at%. The pyridinic and graphitic nitrogen groups are dominant among various N-containing groups in the samples. The 950 °C-activated sample (CANHCS-950) has the largest surface area (2072 m2g−1), pore volume (1.96 cm3g−1), hierarchical micro-mesopore distributions (1.2, 2.6 and 6.2 nm), hollow macropore cores (~91 nm) and highest relative content of pyridinic and graphitic N groups. This triple micro-meso-macropore system could synergistically enhance the activity because macropores could store up the reactant, mesopores could reduce the transport resistance of the reactants to the active sites, and micropores could be in favor of the accumulation of ions. Therefore, the CANHCS-950 with optimized structure shows the optimal and comparable oxygen reduction reaction (ORR) activity but superior methanol tolerance and long-term durability to commercial Pt/C with a 4e−-dominant transfer pathway in alkaline media. These excellent properties in combination with good stability and recyclability make CANHCSs among the most promising metal-free ORR electrocatalysts reported so far in practical applications.