Accelerated electron and mass transfer through constructing H2WO4/Ti3C2/g-C3N4 Z-scheme photocatalyst for environmental remediation.

The catalytic efficiency of photocatalysts highly depends on electron transport and mass transfer. Herein, we designed and prepared an effective H2WO4/Ti3C2/g-C3N4 (HTC) Z-scheme heterojunction through interfacial engineering strategy. The results manifested that 97.4% of Cr(VI) (80 µM, 50 mL) could be removed by HTC heterojunction within 10 min under visible light irradiation. The reduction rate constant of Cr(VI) for H2WO4/g-C3N4 (HC) heterojunction increased by a factor of 21 after introducing the conductive Ti3C2. Moreover, 96% of tetracycline (TC, 10 mg L-1, 50 mL) could be degraded by HTC heterojunction within 30 min. The electronic conductivity and ionic diffusion coefficient of HC heterojunction increased by a factor of 64 and 1064 after adding Ti3C2, respectively. This result indicated that the introduction of highly conductive Ti3C2 significantly improved the electron and mass transfer of the heterojunction. Meanwhile, the HCT heterojunction displayed favorable photocurrent, and keep excellent photostability during the long-term test. Moreover, density functional theory (DFT) calculations demonstrated that the internal electric field (IEF) from g-C3N4 to H2WO4 in HCT heterojunction promotes the combination of the photoinduced electrons in the H2WO4 conduction band (CB) with photoinduced holes in the g-C3N4 valence band (VB), thus accelerating the charge transfer in the HCT Z-scheme heterojunction. The antibacterial efficiency of HTC heterojunction against E. coli and S. aureus could reach up to 98.4% and 99.7%, respectively. The degradation intermediates and the potential degradation mechanism of TC were analyzed and proposed based on the results of HPLC-MS analysis. Moreover, the toxicity of TC and degradation intermediates were estimated by Toxicity Estimation Software (T.E.S.T.) based on quantitative structure-activity relationship (QSAR). This work provided a valuable guideline for designing the effective MXene-based Z-scheme heterojunction for environmental remediation.

S-scheme MOF-on-MOF heterojunctions for enhanced photo-Fenton Cr(VI) reduction and antibacterial effects.

The photocatalytic efficiency is commonly restrained by inferior charge separation rate. Herein, the S-scheme MIL-100(Fe)/NH2-MIL-125(Ti) (MN) photo-Fenton catalyst with the built-in electric field (BEF) was successfully constructed by a simple ball-milling technique. As a result, the MN-3 (the mass ratio of MIL-100(Fe) to NH2-MIL-125(Ti) was 3) composite presented the best visible-light-induced photocatalytic ability, in contrast to pure MIL-100(Fe) and NH2-MIL-125(Ti). The reduction efficiency of Cr(VI) almost reached 100% within 35 min of illumination. Moreover, the MN-3 heterojunction also exhibited the highest antibacterial activity, and about 100% E. coli and more than 90% S. aureus were killed within 60 min of illumination. In photo-Fenton system, In the photo-Fenton system, e-, O2•- and Fe2+ played vital roles for Cr(VI) reduction, and •OH, h+ and O2•- and 1O2 were responsible for sterilization. Additionally, 5 cyclic tests and relevant characterizations confirmed the excellent repeatability and stability of the composite. Also, the S-scheme charge transfer process was put forward. This work offers a novel idea for establishing the MOF-on-MOF photo-Fenton catalyst for high-efficiency environmental mitigation.

The strong interaction and confinement effect of Ag@NH2-MIL-88B for improving the conversion and durability of photocatalytic Cr(VI) reduction in the presence of a hole scavenger.

Selectively regulating active factors in photocatalytic reactions by designing materials is one of the very important factors. Herein, we prepared spindle-like core-shell Ag@NH2-MIL-88B composites (Ag@NM-88) by a two-step hydrothermal method. The as-prepared Ag@NM-88 displayed superior photocatalytic activity for Cr(VI) reduction under LED light, compared with the activities of pure NH2-MIL-88B (NM-88) and Ag/NM-88 (Ag was deposited on NH2-MIL-88B). The core-shell structure Ag@NM-88 was not only beneficial to the absorption of light but also beneficial to the separation of photogenerated e- and h+. More importantly, it was further confirmed by active radical capture experiments and nitroblue tetrazolium (NBT) conversion experiments that the design of the core-shell structure could effectively prevent photogenerated e- from combing with O2 to form •O2-, so that photogenerated e- directly reduced Cr(VI), thereby improving the reaction rate. In addition, it could still maintain good stability after 5 cycles, indicating that the construction of a core-shell structure is also conducive to improving stability. This work provides a strategy for selectively regulating the active components of photocatalysts, and provides new insights into the relationship between interfacial charge transfer and molecular oxygen activation in photocatalytic reduction Cr(VI) systems.

Preparation of novel diperylene-cored polyimide photocatalyst with broad-spectra response and high stability.

A novel polyimide (PI) with broad-spectra response, high photocatalytic activity and stability under super acidic conditions (pH = 0) was synthesized via polymerizing method. Two types of perylene-cored materials (PDIAN and PTCDA) with anhydride and diamine respectively, were applied as precursors for PI polymerization. The as-prepared PI was optimized at 1:1 initial molar ratio of PDIAN to PTCDA. Using common PI (synthesized from melamine and pyromellitic dianhydride) as comparison, the Cr(VI) reduction rate was boosted from 25.4% to 96.6% within 120 min light irradiation. The corresponding rate constant by PI(PDIAN/PTCDA) was estimated to be ca. 11.7 times relative to that by common PI. The boosted performance was ascribed to the strong π-π conjugation from diperylene cores, which can decrease the photoluminescence intensity and electrochemical impedance, so as to promote the separation and transfer of photogenerated electron-hole pairs. In addition, the optimized PI(PDIAN/PTCDA) displayed wide-spectra response, which can still work under 730 nm light. The influencing factors toward Cr(VI) reduction were also clarified to be beneficial at lower pH and increased concentration of hole scavenger. After five cycles at pH 0, the PI still maintained excellent redox activity and structural stability.

PDINH bridged NH2-UiO-66(Zr) Z-scheme heterojunction for promoted photocatalytic Cr(VI) reduction and antibacterial activity.

Z-scheme mechanism was a promising approach to considerably enhance photocatalytic activity. In this work, the PDINH/NH2-UiO-66(Zr) (PNU) heterojunctions were made using a facile ball-milling method. As expect, the optimum PNU-1 composite acted as highly active photocatalyst with 97% Cr(VI) to be reduced within 60 min of LED light illumination. Moreover, the antibacterial rate almost reached 100% for E. coli and S. aureus in 4 h, which was more conspicuous than the others. The wider light absorption range, promoted charge separation because of Z-scheme mechanism and efficient generation of reactive 1O2, •O2-, and •OH contributed greatly to the enhanced photocatalytic activity. Meanwhile, the superior stability and repeatability of the composites were also demonstrated by five cyclic experiments and related physicochemical characterizations. Therefore, this work provides a novel insight for designing high-efficiency Z-scheme heterostructures between MOFs and organic PDINH for wastewater remediation.

Pd(II)-Catalyzed Direct γ-C(sp3)-H Arylation between Free ß2-Amino Esters and ß3-Amino Esters and Aryl Iodides Using a Catalytic Transient Directing Group.

Pd(II)-catalyzed direct γ-C(sp3)-H arylation coupling with free ß2-amino esters and ß3-amino esters using a commercially available catalytic transient directing group has been developed. This approach features high efficiency, broad substrate tolerance, easily accessible starting materials, and mild reaction conditions.

Ru(ii)-catalyzed C6-selective C-H acylmethylation of pyridones using sulfoxonium ylides as carbene precursors.

In this study, we describe a method using sulfoxonium ylides as carbene precursors to achieve C6-selective acylmethylation of pyridones catalyzed by a ruthenium(ii) complex. This approach featured mild reaction conditions, moderate to excellent yields, high step economy, and had excellent functional group tolerance with good site selectivity. Besides, gram-scale preparation, synthetic utility, and mechanistic studies were conducted. It offers a direct and efficient way to synthesize pyridone derivatives.