Tuning the Anisotropic Facet of Lead Chromate Photocatalysts to Promote Spatial Charge Separation

Modeled Single-Atomic-Site Pt Catalyst with Well-Defined Coordination Structure for Hydrosilylation Reaction

Single-atom-site (SAS) catalysts exhibit superior activity in catalytic reactions, and their isolated active sites are anticipated to serve as an ideal platform for mechanistic investigations. However, the coordination environment of SAS catalyst synthesized via pyrolysis is challenging to control, and the active sites are randomly distributed, posing challenges for structure-activity relationship studies. Therefore, the development of model catalysts featuring well-defined coordination structures remains highly desirable but challenging. Herein, a Pt1C48H61P2Cl SAS catalyst is synthesized by an in situ reduction-assembly strategy, serving as a modeled Pt-SAS catalyst with a precisely defined coordination structure. The structure is confirmed as Pt-P2C1Cl1 by single-crystal X-ray diffraction and X-ray absorption spectroscopy. Under solvent-free conditions, this catalyst achieves 98% conversion and >99% selectivity in anti-Markovnikov alkene hydrosilylation within 1 h and can exhibit good recyclability. Density functional theory (DFT) calculations revealed that the synthesized Pt-SAS catalyst exhibits a significantly reduced free energy barrier for the hydrosilylation reaction compared to the traditional Pt (111) surface, which can be attributed to weaker interactions during the oxidative addition step, enabling easier product desorption.

Crystal-Facet-Controlled Internal Electric Field in MOF/COF Heterojunction Towards Efficient Photocatalytic Overall Water Splitting

Covalently integrating two type of crystalline porous materials, metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), to form heterostructure photocatalysts inheriting their structural merits has shown inherent advantages in hydrogen evolution reaction. However, how to control the internal electric field in aimed MOF/COF heterojunction to achieve an improved photocatalytic activity is still ambiguous. Herein, for the first time, we report a rational control of the internal electric field in MOF/COF heterojunction by engineering the crystal facet of MOFs to achieve enhanced photocatalytic overall water splitting (OWS) activity. A new type of covalently connected MOF/COF photocatalytic system based on NH2-MIL-125(Ti) and TpBpy-COF was synthesized. As confirmed, the exposed crystal facet of MOFs greatly affected the resultant activity of MOF/COF system. The combination of decahedron NH2-MIL-125(Ti) and TpBpy-COF shows an optimal OWS activity with the H2 and O2 evolution rates of 331.6 and 165.7 μmol g-1 h-1 under visible light, respectively, which is the best performance in COFs or COF-based photocatalyst at present. The great influence of formed anisotropic facets on internal electric field of the S-scheme MOF/COF heterojunction interface is fully confirmed by various characterizations, and the active crystal facet of NH2-MIL-125(Ti) for water oxidation reaction is further proved.

Proton-Mediated Topological Interlayer Shift in 2D Covalent Organic Frameworks for Efficient Photocatalysis

The interlayer carriers dynamics are of significance in optoelectronic applications of 2D donor-acceptor (D-A) covalent organic frameworks (COFs), while are challenged by the delicate control over the inherently variable and sensitive interlayer interaction. Present work demonstrates an efficient proton-mediation strategy that allows for the precise regulation of interlayer shift of 2D D-A COFs for facilitated charge transfer and exciton dissociation. Exemplified by three imine-linked D-A COFs (IMDA), mild proton-mediation generates an eclipsed AA stacking (IMDA-AA) featuring in-plane D-A pairs and fully overlapping D-A π-conjugations, while excessive proton-mediation disrupts these conjugations, resulting in a slipped AA stacking (IMDA-SAA) with out-of-plane D-A pairs. Further analysis reveals that the interlayer topology of eclipsed AA stacking of IMDA favors for the synergistically optimized charge transfer dynamics, including enhanced intralayer charge transport with reduced exciton binding energy, and boosted interlayer exciton dissociation. IMDA-AA COF delivers an improved hydrogen evolution rate up to 171.2 mmol g-1h-1 under visible light illumination in the presence of 1.5 wt.% Pt co-catalysts, which is as far as is known the highest value among the reports of 2D COFs based photocatalysis. Present work will provide an important avenue of addressing the topology-governed charge transfer dynamics within COFs for solar energy conversion.

Crystal-Facet Engineering of Mesoporous CuS Cascade Nanoreactors Enhances Photocatalytic C-C Coupling of CO2-to-C2H4

Crystal-facet heterojunction engineering of mesoporous nanoreactors with highly redox-active represents an efficacious strategy for the transformation of CO2 into valuable C2 products (e.g., C2H4). Herein, hollow mesoporous cube-like CuS nanoreactors (~860 nm) with controlled anisotropic crystal-facets are prepared through an interfacial-confined ion dynamic migration-rearrangement strategy. The regulation of the S2- ion concentration facilitates the modulation of the highly active (110) to (100) crystal-facet ratios from 0.119 to 0.288, and induces the formation of anisotropic crystal-facet heterojunctions. The controllable crystal-facet heterojunctions trigger the directional charge carrier migration, and are accompanied with the formation of tandem S-defect sites (Cu0-S1@S3). Both of them promote the efficient electron-hole pair dissociation and attain asymmetric C-C coupling. The hollow mesoporous CuS nanoreactors with optimized crystal-facet ratio of 0.224 (HMe-CuS-3) deliver a high selectivity of 72.7 % for the photocatalytic reduction of CO2 to acetylene (C2H2). Further constructed Au-(110) and Co3O4-(100) spatially separated cascade nanoreactors (SS-Au@Co3O4-CuS) achieve CO2-C2H4 photoreduction, in which the Co-sites enhance H2O dissociation to provide protons and the protonation of *CO to *COH. The *COH is further captured by Au-sites to accomplish the asymmetric *CO-*COH coupling and subsequent protonation, ensuring a high C2H4 generation rate of 4.11 μmol/g/h with a selectivity as high as 90.6 %.

Synthesis of PbCrO4 nanorods-Ti3C2Tx MXene composites: A sensitive photoelectrochemical sensor for the detection of cysteine in human blood serum

BACKGROUND

l-cysteine plays an important role in protein synthesis, osmoregulation, detoxification, nervous system function, and antioxidant process. Low levels of cysteine are associated with various diseases like cardiovascular diseases, ischemic stroke, neurological disorders, diabetes, cancer like lung and colorectal cancer, renal dysfunction-linked conditions, and vitiligo. Therefore, it is of great significance to develop a rapid and accurate method for the determination of cysteine concentration.

RESULTS

A photoelectrochemical (PEC) biosensor based on PbCrO4-MXene composites is proposed MXene for the determination of l-cysteine. The original PbCrO4 nanorods are synthesized via a redox reaction that occurred between Pb2+ and K2Cr2O7 in a weakly acidic environment using a hydrothermal approach. The PbCrO4 nanorods show outstanding PEC performance in the catalytic oxidation of l-cysteine. The introduction of Ti3C2Tx MXene nanosheets on PbCrO4 nanorods enables the formation of the local Schottky junction to efficiently improve charge transport and charge separation of PbCrO4 nanorods, achieving excellent catalytic performance. The PbCrO4-MXene composites be used as a photoelectrocatalyst for rapid and sensitive detection of l-cysteine in the human body. Compared with the traditional PEC sensor, this sensor based on PbCrO4-MXene composites can significantly improve the catalytic performance of PEC, showing a better response to l-cysteine. This PEC sensor shows a low limit of detection (LOD) of 0.23 μM for l-cysteine, and a wide linear range of 0.01-18 mM, exceeding expectations compared to previously published papers.

SIGNIFICANCE

Our PEC sensor has been successfully used for the detection of l-cysteine in human blood serum. This work provides a new inspiration for the great practical application of PEC sensors in medicine and clinical diagnosis fields.

Toward Efficient Utilization of Photogenerated Charge Carriers in Photoelectrochemical Systems: Engineering Strategies from the Atomic Level to Configuration

Photoelectrochemical (PEC) systems are essential for solar energy conversion, addressing critical energy and environmental issues. However, the low efficiency in utilizing photogenerated charge carriers significantly limits overall energy conversion. Consequently, there is a growing focus on developing strategies to enhance photoelectrode performance. This review systematically explores recent advancements in PEC system modifications, spanning from atomic and nanoscopic levels to configuration engineering. We delve into the relationships between PEC structures, intrinsic properties, kinetics of photogenerated charge carriers, and their utilization. Additionally, we propose future directions and perspectives for developing more efficient PEC systems, offering valuable insights into potential innovations in the field.

Anisotropic Charge Migration on Perovskite Oxysulfide for Boosting Photocatalytic Overall Water Splitting

The synthesis of photocatalysts with both broad light absorption and efficient charge separation is significant for a high solar energy conversion, which still remains to be a challenge. Herein, a narrow-bandgap Y2Ti2O5S2 (YTOS) oxysulfide nanosheet coexposed with defined {101} and {001} facets synthesized by a flux-assisted solid-state reaction was revealed to display the character of an anisotropic charge migration. The selective photodeposition of cocatalysts demonstrated that the {101} and {001} surfaces of YTOS nanosheets were the reduction and oxidation regions during photocatalysis, respectively. Density functional theory (DFT) calculations indicated a band energy level difference between the {101} and {001} facets of YTOS, which contributes to the anisotropic charge migration between them. The exposed Ti atoms on the {101} surface and S atoms on the {001} surface were identified, respectively, as reducing and oxidizing centers of YTOS nanosheets. This anisotropic charge migration generated a built-in electric field between these two facets, quantified by spatially resolved surface photovoltage microscopy, the intensity of which was found to be highly correlated with photocatalytic H2 production activity of YTOS, especially exhibiting a high apparent quantum yield of 18.2% (420 nm) after on-site modification of a Pt@Au cocatalyst assisted by Na2S-Na2SO3 hole scavengers. In conjunction with an oxygen-production photocatalyst and a [Co(bpy)3]2+/3+ redox shuttle, the YTOS nanosheets achieved a solar-to-hydrogen conversion efficiency of 0.15% via a Z-scheme overall water splitting. Our work is the first to confirm anisotropic charge migration in a perovskite oxysulfide photocatalyst, which is crucial for enhancing charge separation and surface catalytic efficiency in this material.

Acquiring Charge-Transfer-Featured Single-Molecule Ultralong Organic Room Temperature Phosphorescence via Through-Space Electronic Coupling

Although long-lived triplet charge-transfer (3 CT) state with high energy level has gained significant attention, the development of organic small molecules capable of achieving such states remains a major challenge. Herein, by using the through-space electronic coupling effect, we have developed a compound, namely NIC-DMAC, which has a long-lived 3 CT state at the single-molecule level with a lifetime of 210 ms and a high energy level of up to 2.50 eV. Through a combination of experimental and computational approaches, we have elucidated the photophysical processes of NIC-DMAC, which involve sequential transitions from the first singlet excited state (S1 ) that shows a 1 CT character to the first triplet excited state (T1 ) that exhibits a local excited state feature (3 LE), and then to the second triplet excited state (T2 ) that shows a 3 CT character (i.e., S1 (1 CT)→T1 (3 LE)→T2 (3 CT)). The long lifetime and high energy level of its 3 CT state have enabled NIC-DMAC as an initiator for photocuring in double patterning applications.

A Facile Design for Water-Oxidation Molecular Catalysts Precise Assembling on Photoanodes

Regulating the interfacial charge transfer behavior between cocatalysts and semiconductors remains a critical challenge for attaining efficient photoelectrochemical water oxidation reactions. Herein, using bismuth vanadate (BiVO4 ) photoanode as a model, it introduces an Au binding bridge as holes transfer channels onto the surfaces of BiVO4 , and the cyano-functionalized cobalt cubane (Co4 O4 ) molecules are preferentially immobilized on the Au bridge due to the strong adsorption of cyano groups with Au nanoparticles. This orchestrated arrangement facilitates the seamless transfer of photogenerated holes from BiVO4 to Co4 O4 molecules, forming an orderly charge transfer pathway connecting the light-absorbing layer to reactive sites. An exciting photocurrent density of 5.06 mA cm-2 at 1.23 V versus the reversible hydrogen electrode (3.4 times that of BiVO4 ) is obtained by the Co4 O4 @Au(A)/BiVO4 photoanode, where the surface charge recombination is almost completely suppressed accompanied by a surface charge transfer efficiency over 95%. This work represents a promising strategy for accelerating interfacial charge transfer and achieving efficient photoelectrochemical water oxidation reaction.

Effect of low molecular weight organic acids on the lead and chromium release from widely-used lead chromate pigments under sunlight irradiation

Lead chromate pigments are commonly used yellow inorganic pigments. They can pose environmental risks as they contain toxic heavy metals lead and chromium. Low molecular weight organic acids (LMWOAs), as widespread dissolved organic matter (DOM), affect the lead and chromium release from the pigment in water. In this work, the role of LMWOAs in the photodissolution of commercial lead chromate pigment was investigated. The pigment underwent significant photodissolution under simulated sunlight exposure with LMWOAs, and subsequently released Cr(III) and Pb(II). The photodissolution process is caused by the reduction of Cr(VI) by photogenerated electrons of the lead chromate pigment. The LMWOAs promoted photodissolution of the pigment by improving the electron-hole separation. The formation of Cr(III)-contained compounds leads to a slower release of chromium than lead. The photodissolution kinetics increase with decreasing pH and increasing LMWOAs concentration. The photodissolution of lead chromate pigment was basically positively related to the total number of hydroxyl and carboxyl groups in LMWOAs. The LMWOAs with stronger affinity to lead chromate pigment, lower adiabatic ionization potential (AIP) and higher energy of the highest occupied molecular orbital (EHOMO) are favorable to Cr(VI) reduction by photogenerated electrons and pigment photodissolution. 2.39% of chromium and 10.34% of lead released from the lead chromate pigment in natural conditions during a 6-h sunlight exposure. This study revealed the photodissolution mechanism of lead chromate pigment mediated by LMWOAs with different molecular structures, which helps understand the environmental photochemical behavior of the pigment. The present results emphasize the important role of DOM in the heavy metals release from commercial inorganic pigments.

Bottom-up Synthesis of Single-Crystalline Poly (Triazine Imide) Nanosheets for Photocatalytic Overall Water Splitting

Poly (triazine imide) (PTI/Li+ Cl- ), one of the crystalline versions of polymeric carbon nitrides, holds great promise for photocatalytic overall water splitting. In principle, the photocatalytic activity of PTI/Li+ Cl- is closely related to the morphology, which could be reasonably tailored by the modulation of the polycondensation process. Herein, we demonstrate that the hexagonal prisms of PTI/Li+ Cl- could be converted to hexagonal nanosheets by adjusting the binary eutectic salts from LiCl/KCl or NaCl/LiCl to ternary LiCl/KCl/NaCl. Results reveal that the extension of in-plane conjugation is preferred, when the polymerisation was performed in the presence of ternary eutectic salts. The hexagonal nanosheets bears longer lifetimes of charge carriers than that of hexagonal prisms due to lower intensity of structure defects and shorter hopping distance of charge carriers along the stacking direction of triazine nanosheets. The optimized hexagonal nanosheets exhibits a record apparent quantum yield value of 25 % (λ=365 nm) for solar hydrogen production by one-step excitation overall water splitting.