Integrating Enrichment, Reduction, and Oxidation Sites in One System for Artificial Photosynthetic Diluted CO2 Reduction.

Artificial photosynthetic diluted CO2 reduction directly driven by natural sunlight is a challenging, but promising way to realize carbon-resources recycling utilization. Herein, a three-in-one photocatalytic system of CO2 enrichment, CO2 reduction and H2 O oxidation sites is designed for diluted CO2 reduction. A Zn-Salen-based covalent organic framework (Zn-S-COF) with oxidation and reductive sites is synthesized; then, ionic liquids (ILs) are loaded into the pores. As a result, [Emim]BF4 @Zn-S-COF shows a visible-light-driven CO2 -to-CO conversion rate of 105.88 µmol g-1 h-1 under diluted CO2 (15%) atmosphere, even superior than most photocatalysts in high concentrations CO2 . Moreover, natural sunlight driven diluted CO2 reduction rate also reaches 126.51 µmol g-1 in 5 h. Further experiments and theoretical calculations reveal that the triazine ring in the Zn-S-COF promotes the activity of H2 O oxidation and CO2 reduction sites, and the loaded ILs provide an enriched CO2 atmosphere, realizing the efficient photocatalytic activity in diluted CO2 reduction.

Constructing tightly integrated conductive metal-organic framework/covalent triazine framework heterostructure by coordination bonds for photocatalytic hydrogen evolution.

The construction of tightly integrated heterostructures with metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) has been confirmed to be an effective way for improved hydrogen evolution. However, the reported tightly integrated MOF/COF hybrids were usually limited to the covalent connection of COFs with aldehyde groups and NH2-MOF via Schiff base reaction, restricting the development of MOF/COF hybrids. Herein, a covalent triazine framework (CTF-1), a subtype of crystalline COFs, was integrated with a conductive two-dimensional (2D) MOF (Ni-CAT-1) by a novel coordinating connection mode for significantly enhanced visible-light-driven hydrogen evolution. The terminal amidine groups in the CTF-1 layers offer dual N sites for the coordination of metal ions, which provides the potential of coordinating connection between CTF-1 and Ni-CAT-1. The conductive 2D Ni-CAT-1 in Ni-CAT-1/CTF-1 hybrids effectively facilitates the separation of photogenerated carriers of CTF-1 component, and the resultant hybrid materials show significantly enhanced photocatalytic hydrogen evolution activity. In particular, the Ni-CAT-1/CTF-1 (1:19) sample exhibits the maximum hydrogen evolution rate of 8.03 mmol g-1h-1, which is about four times higher than that of the parent CTF-1 (1.96 mmol g-1h-1). The enhanced photocatalytic activity of Ni-CAT-1/CTF-1 is mainly attributed to the incorporation of conductive MOF which leads to the formation of a Z-Scheme heterostructure, promoting the electron transfer in hybrid materials. The coordinating combination mode of Ni-CAT-1 and CTF-1 in this work provides a novel strategy for constructing tightly integrated MOF/COF hybrid materials.

Photocatalytic reduction of Cr(VI) over cinder-based nanoneedle in presence of tartaric acid: Synergistic performance and mechanism.

Cr(VI) is a common heavy metal ion, which will seriously harm human body and environment. Therefore, the removal of Cr(VI) has become an attractive topic. In this work, cinder was used as a raw material to synthesize a nanoneedle material: γ-(AlOOH@FeOOH) (γ-Al@Fe). The physicochemical properties of γ-Al@Fe were thoroughly characterized, and its effectiveness as a catalyst for photocatalytic reduction of Cr(VI) was evaluated. The results showed that Cr(VI) could be efficiently reduced by γ-Al@Fe in the presence of tartaric acid (TA) under visible light. The variable factors on the reaction were investigated in detail, and the results showed that under optimal conditions (γ-Al@Fe 0.4 g/L, TA 0.6 g/L, pH 2), Cr(VI) was completely reduced within 7 min. Besides, scavenger experiments and EPR proved that O2• - and CO2• - played a significant role in the photocatalytic reduction of Cr(VI). TA acts as a sacrificial agent to trap the holes and generate strong reducing free radicals: CO2• -. Dissolving O2 could react with electrons to generate O2• -. This work discussed the performance and mechanism of photocatalytic reduction of Cr(VI) in detail, which provided a new idea for the resource utilization of solid waste and the treatment of heavy metal sewage.

Crystallinity-dependent photodegradation of metallic Bi in situ grown on perovskite Bi3TiNbO9 nanosheets toward antibiotic.

Owing to its wide band gap of ~3.2 eV, perovskite Bi3TiNbO9 only absorbs the solar spectrum in the ultraviolet range, which restricts its use as an effective photocatalyst. Here, a controllable and facile reduction strategy was adopted to promote the in-situ growth of metallic Bi in perovskite Bi3TiNbO9 nanosheets. The in-situ growth of metallic Bi extended photoresponse to cover the whole visible region. Adsorption of tetracycline hydrochloride (TC-H) on the surface of Bi3TiNbO9 with in-situ growth of metallic Bi (BTNOOV-Bi0) was dramatically enhanced, while BTNOOV-Bi0 exhibited a superior photocatalytic performance for tetracycline hydrochloride (TC-H) degradation under visible light irradiation with the degradation rate of 5 times higher than that of pristine Bi3TiNbO9. Moreover, the degradation activity was strongly dependent on the crystallinity of metallic Bi phase in BTNOOV-Bi0 samples. On the basis of experiment results, the visible-light driven catalytic mechanism of BTNOOV-Bi0 was elucidated. Besides, the in-situ growth of metallic Bi was also introduced in perovskite Bi5FeTi3O15, resulting in an enhanced photocatalytic activity, which indicated an enormous potential of this strategy in semiconductor structure tuning. Our study provides an effective approach to boost the performance of photocatalysts for solar-energy conversion.

Surface structure tuning of BiOCl nanosheets by the sequential introduction of oxygen vacancies, PO43- and Ag+ for boosting photodegradation of tetracycline hydrochloride.

The surface structure significantly impacts the physicochemical properties of semiconductors. Constructing heterojunction is a universal approach to tune surface structure, which can effectively accelerate the charge transfer at the interface. Here, BiOCl nanosheets which occupy high ratio of surface atoms to entire atoms were used as a model photocatalyst, and a strategy was proposed to tune its surface structure by sequential introduction of oxygen vacancies, PO43- and Ag+ on surface of BiOCl nanosheets. In order to inhibit the overgrowth of heterogeneous component, the excess PO43- was timely removed by centrifugation before adding Ag+. As a result, the as-obtained optimal sample which was confirmed to be a composite composed of BiOCl, BiPO4 and AgCl showed superior photocatalytic activity for tetracycline hydrochloride degradation with the rate of 38 times higher than that of pristine BiOCl, which was mainly attributed to the quick migration of photongenerated carrier. The active species h+ and •O2- played a vital role in this degradation process. Our strategy not only greatly saved investment of noble metal Ag, but also provide superior stability. On the basis of experimental results and density functional theory calculation, the visible-light driven catalytic mechanism was revealed.

Preparation of a new Fenton-like catalyst from red mud using molasses wastewater as partial acidifying agent.

Using molasses wastewater as partial acidifying agent, a new Fenton-like catalyst (ACRM sm ) was prepared through a simple process of acidification and calcination using red mud as main material. With molasses wastewater, both the free alkali and the chemically bonded alkali in red mud were effectively removed under the action of H2SO4 and molasses wastewater, and the prepared ACRM sm was a near-neutral catalyst. The ACRM sm preparation conditions were as follows: for 3 g of red mud, 9 mL of 0.7 mol/L H2SO4 plus 2 g of molasses wastewater as the acidifying agent, calcination temperature 573 K, and calcination time 1 h. Iron phase of ACRM sm was mainly α-Fe2O3 and trace amount of carbon existed in ACRM sm . The addition of molasses wastewater not only effectively reduced the consumption of H2SO4 in acidification of red mud but also resulted in the generation of carbon and significantly improved the distribution of macropore in prepared ACRM sm . It was found that near-neutral pH of catalyst, generated carbon, and wide distribution of macropore were the main reasons for the high catalytic activity of ACRM sm . The generated carbon and wide distribution of macropore were entirely due to the molasses wastewater added. In degradation of orange II, ACRM sm retained most of its catalytic stability and activity after five recycling times, indicating ACRM sm had an excellent long-term stability in the Fenton-like process. Furthermore, the performance test of settling showed ACRM sm had an excellent settleability. ACRMsm was a safe and green catalytic material used in Fenton-like oxidation for wastewater treatment.

Preparation and application of acidified/calcined red mud catalyst for catalytic degradation of butyl xanthate in Fenton-like process.

Acidified/calcined red mud (ACRM), a novel catalyst used in Fenton-like process, was prepared by acidification and calcination of red mud (RM). Catalyst characterization showed that iron phase of ACRM was mainly α-Fe2O3 and ACRM was a porous material with rough surface and loose structure. Degradation of butyl xanthate in Fenton-like process catalyzed by ACRM was investigated. Butyl xanthate was effectively degraded, and the degradation of butyl xanthate was well fitted by second order kinetic model. ACRM had an excellent long-term stability in a Fenton-like process. The possible mechanisms of hydroxyl radical production and butyl xanthate degradation in a Fenton-like process catalyzed by ACRM were presented.