A self-biased fuel cell with TiO2/g-C3N4 anode catalyzed alkaline pollutant degradation with light and without light—What is the degradation mechanism?

Successful bio-electrochemical treatment of nitrogenous mariculture wastewater by enhancing nitrogen removal via synergy of algae and cathodic photo-electro-catalysis

Systems with catalytic cathode in microbial fuel cell can achieve high treatment efficiency enhanced by the cathode. Such bio-electrochemical systems have potential applications in treating high-salinity nitrogenous mariculture wastewater. For sustainable development of the mariculture industry, enhancing inorganic nitrogen removal is of vital importance due to the low carbon to nitrogen (C/N) ratio of wastewater and strict discharge standard. Herein, simulated mariculture wastewater (high salinity, low COD/N ratio of 0.5-1.0) was successfully treated in an integrated self-biased bio-electrochemical system, with catalyst (TiO₂/Co-WO₃/SiC) on the cathode and natural-grown algae in the cathode chamber. Satisfactory nitrogen removal (94.05% NH₄⁺-N and 77.35% inorganic nitrogen) and favorable 76.66% removal of organics (UV₂₅₄) were both achieved, with visible light illumination. The NH₄⁺-N in the effluent was below 2 mg L^-1. The synergy of bacteria, algae and cathode, promoted pollutant removal, and made the system sustainable and efficient in treating mariculture wastewater.

Enhanced reduction and oxidation capability over the CeO2/g-C3N4 hybrid through surface carboxylation: performance and mechanism

The charge separation efficiency of the CeO₂/g-C₃N₄ heterojunction was greatly enhanced through surface carboxylation of the g-C₃N₄ substrate.

Enhancement of photoelectrochemical organics degradation and power generation by electrodeposited coatings of g-C3N4 and graphene on TiO2 nanotube arrays

New g-C₃N₄ coatings obtained via electropolymerization (EP) of melamine followed by a heat treatment and graphene oxide (GO) coatings based on combining GO sheets via EP of GO phenolic groups are used to improve the performance of photoanodes composed of TiO₂ nanotube arrays towards the photoelectrochemical (PEC) oxidation of methanol. This process, as examined in Na₂CO₃ solution (pH 11.4) for the two types of coatings and serving as a model for the degradation of an organic pollutant, demonstrates enhanced PEC performance as compared to that obtained using electrochemically reduced GO coatings. PEC oxidation currents obtained with 1 M methanol reach saturation at potentials as low as ∼-0.4 V vs. Ag/AgCl, with the highest saturation current density of ∼2.6 mA cm^-2 and photon-to-current efficiency of 52% as observed for the new TiO₂NTs/g-C₃N₄ photoanodes. Electrochemical impedance spectroscopy measurements for these photoanodes show a charge transfer resistance one order of magnitude lower than that obtained by the other types of coatings. This indicates an enhanced charge separation ability for the photogenerated electron-hole pairs and faster interfacial charge transfer between the electron donor (methanol) and acceptor (holes). It is also demonstrated that the process of organics degradation can be achieved not only via an applied potential but also in a galvanic photofuelcell with methanol and oxygen serving as the fuel and oxidant, respectively. The power densities achieved with the electrochemically prepared g-C₃N₄ photoanodes (∼0.5 mW cm^-2) are at least one order of magnitude higher than those reported for other TiO₂-based systems.

Synergetic Effect of Ti3+ and Oxygen Doping on Enhancing Photoelectrochemical and Photocatalytic Properties of TiO2/g-C3N4 Heterojunctions

To improve the utilization of visible light and reduce photogenerated electron/hole recombination, Ti³⁺ self-doped TiO₂/oxygen-doped graphitic carbon nitride (Ti³⁺-TiO₂/O-g-C₃N₄) heterojunctions were prepared via hydrothermal treatment of a mixture of g-C₃N₄ and titanium oxohydride sol obtained from the reaction of TiH₂ with H₂O₂. In this way, exfoliated O-g-C₃N₄ and Ti³⁺-TiO₂ nanoparticles were obtained. Simultaneously, strong bonding was formed between Ti³⁺-TiO₂ nanoparticles and exfoliated O-g-C₃N₄ during the hydrothermal process. Charge transfer and recombination processes were characterized by transient photocurrent responses, electrochemical impedance test, and photoluminescence spectroscopy. The photocatalytic performances were investigated through rhodamine B degradation test under an irradiation source based on 30 W cold visible-light-emitting diode. The highest visible-light photoelectrochemical and photocatalytic activities were observed from the heterojunction with 1:2 mass ratio of Ti³⁺-TiO₂ to O-g-C₃N₄. The photodegradation reaction rate constant based on this heterojuction is 0.0356 min^-1, which is 3.87 and 4.56 times higher than those of pristine Ti³⁺-TiO₂ and pure g-C₃N₄, respectively. The remarkably high photoelectrochemical and photocatalytic performances of the heterojunctions are mainly attributed to the synergetic effect of efficient photogenerated electron-hole separation, decreased electron transfer resistance from interfacial chemical hydroxy residue bonds, and oxidizing groups originating from Ti³⁺-TiO₂ and O-g-C₃N₄.