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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.

Complex surface dynamics is the key to limit the photoelectrochemical performance of hematite, while its core content is the hole trapping and release by surface traps. Deep traps are accompanied by extremely fast capture rates and extremely slow release rates, which severely suppress the hole transport process. Herein, we proposed a unique method to progressively convert deep traps on the hematite surface for fast hole transfer via in situ one-step metal organic framework modification. This stepwise deep-trap passivation is achieved by hematite corrosion first on the surface and subsequent construction of a porous titanium layer. The gentle trap finishing helps prevent surface losses caused by excessively intense trap passivation. The hematite corrosion can initially passivate 80% of the surface deep traps, while the subsequent porous titanium layer can completely passivate the deep traps. In addition, the accurate optimization of the porous titanium layer can reconstruct the benign shallow traps on the surface, acting as superior oxygen evolution reaction active sites. This sophisticated surface-trap adjustment is accompanied by the rapid reduction of deep traps and the gradual increase of shallow traps, obtaining a superior surface state that is conducive to charge transport and interface catalysis. The obtained treated hematite yields a photocurrent density of 3.08 mA·cm–2at 1.23 VRHE, increased by 570% compared to the pristine hematite.

Excessive emissions of ammonia and organic pollutants have been a challenge for conventional wastewater treatment. Chlorine oxide radical-mediated advanced oxidation processes (ClO•-AOPs) have recently garnered significant interest for their benefits, such as ease of operation and high selectivity. This review presents the latest insights into the removal mechanism of ammonia and organic pollutants by ClO•, especially focusing on the similarities and distinctions between representative radicals. ClO• has a redox potential of 1.5V and is formed via photo/photoelectrochemical and electrochemical reactions, whose concentration is significantly higher than that of Cl• and OH•. ClO• shows selective reactivity toward compounds with electron-rich moieties at higher second-order rate constants, and the major degradation mechanism is electron transfer. The reaction kinetics, free radical quenching, electron paramagnetic resonance, and radical probes are reviewed. ClO• is not easily consumed by water matrix components (carbonate and dissolved organic matter (DOM)), and its proper potential can abate the chlorinated disinfection byproducts after treatment. Lastly, we offer recommendations for further investigation of ClO• in the fields of photo/photoelectrocatalysis and electrocatalysis, as well as emphasize essential topics for future research.

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.

As the primary source of nitrogen pollutants in domestic sewage, urine is also an alternative for H2production via electrochemical processes. However, it suffers from sluggish kinetics and noble-metal catalyst requirement. Here, we report a non-precious ultrathin NiFe-layered double hydroxide catalyst for the remarkable conversion of urea into N2and H2, which is in situ grown on a Ni foam via ultrasonic self-etching in Fe3+/ethylene glycol (EG). EG regulates the etching rate of Fe3+, resulting in an ultrathin nanosheet structure with the aid of ultrasonication. This structure dramatically promotes the dehydrogenation process via decreasing the nanolayer thickness from 120 to 3.4 nm and leads to a 4.8-fold increase in the generation of active sites. It exhibits record urea oxidation kinetics (390.8 mA·cm–2at 1.5 V vs RHE) with excellent stability (120 h), which is 11.8 times better than that of commercial Pt/C catalyst (33.1 mA·cm–2). Tests with real urine at 20 mA cm–2achieve 74% total nitrogen removal and 2853 μmol·h–1of H2production. This study provides an attractive landscape for producing H2by consuming urine biowastes.

Hydrogen peroxide (H2O2) in situelectrosynthesis by O2reduction reaction is a promising alternative to the conventional Fenton treatment of refractory wastewater. However, O2mass transfer limitation, cathodic catalyst selectivity, and electron transfer in O2reduction remain major engineering obstacles. Here, we have proposed a systematic solution for efficient H2O2generation and its electro-Fenton (EF) application for refractory organic degradation based on the fabrication of a novel ZrO2/CMK-3/PTFE cathode, in which polytetrafluoroethylene (PTFE) acted as a hydrophobic modifier to strengthen the O2mass transfer, ZrO2was adopted as a hydrophilic modifier to enhance the electron transfer of O2reduction, and mesoporous carbon (CMK-3) was utilized as a catalyst substrate to provide catalytic active sites. Moreover, feasible mass transfer of O2from the hydrophobic to the hydrophilic layer was designed to increase the contact between O2and the reaction interface. The H2O2yield of the ZrO2/CMK-3/PTFE cathode was significantly improved by approximately 7.56 times compared to that of the conventional gas diffusion cathode under the same conditions. The H2O2generation rate and Faraday efficiency reached 125.98 mg·cm−2·h−1(normalized to 5674.04 mmol·g−1·h−1by catalyst loading) and 78.24% at −1.3 V versus standard hydrogen electrode (current density of −252 mA·cm−2), respectively. The high H2O2yield ensured that sufficient ·OH was produced for excellent EF performance, resulting in a degradation efficiency of over 96% for refractory organics. This study offers a novel engineering solution for the efficient treatment of refractory wastewater using EF technology based on in situhigh-yield H2O2electrosynthesis.

Generally, the loading of oxygen evolution catalyst (OEC) must be carefully controlled to an extremely thin level or the photo-generated holes will mainly charge the catalyst rather than oxidizing water. To overcome the extreme sensitivity of charge transport to catalyst thickness, we proposed the iron valence state regulating on hematite to negatively shift the surface defect state, thereby suppressing the severe OEC charging. In detail, a fluorine layer (FeOxFy) was inserted between Fe2O3and OEC (ZIF-67) to reduce the oxidation state of iron atoms, forming a case where only part of Co(II) can be oxidized (build a rapid Co(II)/Co(III) cycle). Even in the case of thicker OEC (~10 nm), Fe2O3@F@ZIF-67 exhibits increased photocurrent density of 2.56 mA cm−2at 1.23VRHE(~170% higher than Fe2O3@ZIF-67), accompanied by a rapid decrease in sensitivity to OEC loading. Above pretreatment not only relaxed the catalyst process requirements, but also provide new insights into interfacial catalysis process.