Bifunctional Carbon Nitride Exhibiting both Enhanced Photoactivity and Residual Catalytic Activity in the Post-Irradiation Dark Period

π-electron injection activated dormant ligands in graphitic carbon nitride for efficient and stable uranium extraction

Graphitic carbon nitride (CN) as an adsorbent exhibit promising potential for the removal of uranium in water. However, the lack of active sites seriously restricts its practical application. In contrast to the traditional method of introducing new ligands, we propose a strategy to activate original ligands on CN by injecting π electrons, which can be realized by grafting 4-phenoxyphenol (PP) on CN (PCN). Compared with CN, the maximum adsorption capacity of PCN for uranium increased from 150.9 mg/g to 380.6 mg/g. Furthermore, PCN maintains good adsorption properties over a wide range of uranium concentrations (1 ∼ 60 mg/L) and pH (4 ∼ 8). After 5 consecutive cycles, PCN exhibited sustained uranium removal performance with a little of losses. The experimental and theoretical results show that the enhancement of adsorption performance is mainly due to the ligands activation of CN by delocalization of π electrons from PP. Furthermore, this activation can be enhanced by irradiation, as the CN can be photoexcited to provide additional photoelectrons for PP. As a result, dormant ligands such as N-CN, C-O-C, C-N-H and N-(C)3 can be activated to participate in coordination with uranium. This work provides theoretical guidance for the design and preparation of high efficiency uranium adsorbent.

Tunable CO2-to-syngas conversion via strong electronic coupling in S-scheme ZnGa2O4/g-C3N4 photocatalysts

The conversion of CO2 into syngas, a mixture of CO and H2, via photocatalytic reduction, is a promising approach towards achieving a sustainable carbon economy. However, the evolution of highly adjustable syngas, particularly without the use of sacrifice reagents or additional cocatalysts, remains a significant challenge. In this study, a step-scheme (S-scheme) 0D ZnGa2O4 nanodots (∼7 nm) rooted g-C3N4 nanosheets (denoted as ZnGa2O4/C3N4) heterojunction photocatalyst was synthesized vis a facial in-situ growth strategy for efficient CO2-to-syngas conversion. Both experimental and theoretical studies have demonstrated that the polymeric nature of g-C3N4 and highly distributed ZnGa2O4 nanodots synergistically contribute to a strong interaction between metal oxide and C3N4 support. Furthermore, the desirable S-scheme heterojunction in ZnGa2O4/C3N4 efficiently promotes charge separation, enabling strong photoredox ability. As a result, the S-scheme ZnGa2O4/C3N4 exhibited remarkable activity and selectivity in photochemical conversion of CO2 into syngas, with a syngas production rate of up to 103.3 μ mol g-1 h-1, even in the absence of sacrificial agents and cocatalyst. Impressively, the CO/H2 ratio of syngas can be tunable within a wide range from 1:4 to 2:1. This work exemplifies the effectiveness of a meticulously designed S-scheme heterojunction photocatalyst for CO2-to-syngas conversion with adjustable composition, thus paving the way for new possibilities in sustainable energy conversion and utilization.

MXene derived Ti3C2/TiO2/Ag persistent photocatalyst with enhanced electron storage capacity for round-the-clock degradation of organic pollutant

Persistent photocatalysis has garnered significant attention due to its ability to sustain catalytic activity in dark by storing electrons. However, the practical application of persistent photocatalysis is hindered by limited electron storage capacity. Herein, we synthesized and demonstrated that Ti3C2/TiO2/Ag persistent photocatalyst has good electron storage capability. The electron storage capacity of Ti3C2/TiO2/Ag is up to 0.125 μmol/mg, which is 2.5 times that of Ti3C2/TiO2. The enhanced electron storage capacity resulted in improved dark-reaction activity because more electrons react with oxygen to form more radicals, as evidenced by degradation experiments of various organics. Especially, persistent photocatalytic degradation of tetracycline hydrochloride by Ti3C2/TiO2/Ag was achieved under natural outdoor conditions (from 2:00p.m. to 8:00p.m.). Additionally, the aid of oxidants such as peroxymonosulfate (PMS) can further improve the dark-reaction activity. TiO2/Ti3C2/Ag/PMS system exhibits excellent efficacy in removing tetracycline hydrochloride, oxytetracycline, rhodamine b, methyl orange, and methylene blue, with removal rates reaching 79.5 %, 81.4 %, 98.9 %, 99.1 %, and 99.2 %, respectively (15 min of light-reaction and 45 min of dark-reaction). This work provides a new strategy to enhance electron storage capacity and demonstrates that decoupling of light-reaction and dark-reaction may provide a new opportunity for photocatalytic removal of pollutants around the clock.

Nanoarchitecture Manipulation by Polycondensation on KCl Crystals toward Crystalline Lamellar Carbon Nitride for Efficient H2O2 Photoproduction

A lamellar carbon nitride (CN) framework is one of the most promising materials for solar-driven hydrogen peroxide production. The low dielectric constant of the organic CN framework leads to severe recombination of the excitons, and the photon-to-chemical conversion efficiency is thus unsatisfactory. In this work, by polycondensation of the small molecules on the KCl crystal surface, K⁺-incorporated crystalline CN (CNK) frameworks show significantly extended periodicity of the stacking layers and in-plane orderly organized heptazine/triazine units. The crystalline CNK frameworks exhibit a series of favorable photophysical properties, such as enhanced photon absorption, negatively shifted LUMO potentials, and attenuated emissive decay of the excitons. The CNK frameworks thus present remarkable performance in the photocatalytic selective oxygen reduction reaction for hydrogen peroxide production, e.g., CNK framework from the polycondensation of NH₄SCN on the KCl surface could produce hydrogen peroxide at a remarkable reaction rate of 26.7 mmol h^-1 g^-1 with a high apparent quantum yield of 25.0%, which is 23.5 times that on its counterpart synthesized in the absence of KCl. This method is generally applicable to all of the precursors for CN synthesis.

Potassium-Derived Charge Channels in Boron-Doped g-C3N4 Nanosheets for Photocatalytic NO Oxidation and Hydrogen Evolution

The application of graphitic carbon nitride (g-C3N4) in photocatalytic NO oxidation was limited due to severe recombination of photogenerated carriers and low concentration of oxidizing species. In this work, K and B were introduced into the interlayer and in-plane framework of g-C3N4 to address this challenge through the thermal polymerization process. The synthesized K-doped B-g-C3N4 nanosheets exhibited expanded light absorption and low charge recombination efficiency. In addition, the doping of K and B reduced the band gap of g-C3N4, which corresponded to enhanced light absorption. B was introduced into the in-plane structure by replacing C atoms, which adjusted the in-plane electron distribution. K was inserted into the interlayer by binding to the N and C atoms of adjacent layers. K-derived electron transfer channels were constructed, which increased electron delocalization and expanded the π-conjugate system. More electrons were transferred through the interlayer channels and were involved in the reaction process. The severe carrier recombination and weak transfer were improved due to the synergistic effect of K and B doping. K-doped B-g-C3N4 nanosheets exhibited enhanced generation of superoxide radicals and hydroxyl radicals, which played a key role during NO oxidation. The photocatalytic NO oxidation efficiency of codoped g-C3N4 nanosheets reached 61%, which was 2.1 and 1.2 times of that of pristine g-C3N4 and B-doped g-C3N4, respectively. The codoped g-C3N4 sample still exhibited stable photocatalytic NO oxidation efficiency after five cycles. This result provided a potential idea for improving the charge distribution and transfer of layered materials by codoping metallic and nonmetallic elements and for photocatalytic NO oxidation.

Degradation and detoxification of broad-spectrum antibiotics by small molecular intercalated BiOCl under visible light

In view of the increasing threat of overuse of broad-spectrum antibiotics to water environment, here, a series of small molecular intercalated bismuth oxychloride (SBC-X) composite photocatalysts were successfully constructed by a simple stirring synthesis at room temperature. Among them, SBC-0.5 showed excellent photocatalytic performance against the three target broad-spectrum antibiotics in visible light, which was 3.06 times, 5.93 times and 11.64 times higher than that of monomer for degrading tetracycline, norfloxacin and ciprofloxacin, respectively. Through analysis, it was found that the excellent photocatalytic degradation performance of SBC-0.5 was mainly attributed to the greatly improved specific surface area, which increased to 14 times of monomer, providing a large number of reaction sites for the subsequent photocatalytic degradation. Besides, intercalated molecules as charge transfer bridges between nanosheets greatly accelerated the efficiency of photogenerated charge transfer between layers. Free radical trapping experiments and electron spin resonance indicated that superoxide anion radicals played a major role in the photocatalytic degradation, followed by singlet oxygen. Furthermore, nine potential degradation intermediates were identified, and the toxicity was greatly reduced confirmed by ECOSAR software prediction and soybean seed germination and seeding growth experiment. Our work will provide useful information for the purification of wastewater containing antibiotics.