Charge Recombination Rate Research Articles

Controlling Symmetry Breaking Charge Transfer in BODIPY Pairs.

Symmetry breaking charge transfer (SBCT) is a process in which a pair of identical chromophores absorb a photon and use its energy to transfer an electron from one chromophore to the other, breaking the symmetry of the chromophore pair. This excited state phenomenon is observed in photosynthetic organisms where it enables efficient formation of separated charges that ultimately catalyze biosynthesis. SBCT has also been proposed as a means for developing photovoltaics and photocatalytic systems that operate with minimal energy loss. It is known that SBCT in both biological and artificial systems is in part made possible by the local environment in which it occurs, which can move to stabilize the asymmetric SBCT state. However, how environmental degrees of freedom act in concert with steric and structural constraints placed on a chromophore pair to dictate its ability to generate long-lived charge pairs via SBCT remain open topics of investigation.In this Account, we compare a broad series of dipyrrin dimers that are linked by distinct bridging groups to discern how the spatial separation and mutual orientation of linked chromophores and the structural flexibility of their linker each impact SBCT efficiency. Across this material set, we observe a general trend that SBCT is accelerated as the spatial separation between dimer chromophores decreases, consistent with the expectation that the electronic coupling between these units varies exponentially with their separation. However, one key observation is that the rate of charge recombination following SBCT was found to slow with decreasing interchromophore separation, rather than speed up. This stems from an enhancement of the dimer's structural rigidity due to increasing steric repulsion as the length of their linker shrinks. This rigidity further inhibits charge recombination in systems where symmetry has already enforced zero HOMO-LUMO overlap. Additionally, for the forward transfer, the active torsion is shown to increase LUMO-LUMO coupling, allowing for faster SBCT within bridging groups.By understanding trends for how rates of SBCT and charge recombination depend on a dimer's internal structure and its environment, we identify design guidelines for creating artificial systems for driving sustained light-induced charge separation. Such systems can find application in solar energy technologies and photocatalytic applications and can serve as a model for light-induced charge separation in biological systems.

One-Pot Synthesis of SnO2-rGO Nanocomposite for Enhanced Photocatalytic and Anticancer Activity.

Metal oxide and graphene derivative-based nanocomposites (NCs) are attractive to the fields of environmental remediation, optics, and cancer therapy owing to their remarkable physicochemical characteristics. There is limited information on the environmental and biomedical applications of tin oxide-reduced graphene oxide nanocomposites (SnO2-rGO NCs). The goal of this work was to explore the photocatalytic activity and anticancer efficacy of SnO2-rGO NCs. Pure SnO2 NPs and SnO2-rGO NCs were prepared using the one-pot hydrothermal method. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), UV–Vis spectrometry, photoluminescence (PL), and Raman scattering microscopy were applied to characterize the synthesized samples. The crystallite size of the SnO2 NPs slightly increased after rGO doping. TEM and SEM images show that the SnO2 NPs were tightly anchored onto the rGO sheets. The XPS and EDX data confirmed the chemical state and elemental composition of the SnO2-rGO NCs. Optical data suggest that the bandgap energy of the SnO2-rGO NCs was slightly lower than for the pure SnO2 NPs. In comparison to pure SnO2 NPs, the intensity of the PL spectra of the SnO2-rGO NCs was lower, indicating the decrement of the recombination rate of the surfaces charges (e−/h+) after rGO doping. Hence, the degradation efficiency of methylene blue (MB) dye by SnO2-rGO NCs (93%) was almost 2-fold higher than for pure SnO2 NPs (54%). The anticancer efficacy of SnO2-rGO NCs was also almost 1.5-fold higher against human liver cancer (HepG2) and human lung cancer (A549) cells compared to the SnO2 NPs. This study suggests a unique method to improve the photocatalytic activity and anticancer efficacy of SnO2 NPs by fusion with graphene derivatives.

S-scheme g-C3N4/ZnO heterojunction photocatalyst with enhanced photodegradation of azo dye

BackgroundThe low specific surface area (SSA) and high charge recombination rate of g-C3N4 (hereafter referred to as CN) limit its applications for dye photodegradation. A photocatalyst that enhanced the SSA and retarded the charge recombination rate of g-C3N4 was developed in this study. MethodsIn this study, a g-C3N4/ZnO S-scheme heterojunction photocatalyst was prepared via template method. Zeolitic-imidazolate-framework-8 (ZIF8) was used as a template of g-C3N4 and as a precursor of ZnO. This method addressed the two above-mentioned limitations of CN simultaneously. Significant findingsIt was confirmed that when calcination temperature was controlled at 450 °C, g-C3N4/ZnO S-scheme heterojunction was successfully fabricated to enhance the specific surface area and charge separation rate of g-C3N4. CN/ZIF8-450 displayed optimal AR1 decolorization performance (95%), which was 1.6 times higher than that of CN (43%), when the reaction time was 1 h. The excellent performance of CN/ZIF8-450 was attributed to its high specific surface area (182.8 m2/g), 3.4 times higher than that of CN (53.6 m2/g), and low charge recombination rate due to the S-scheme heterojunction. The main reaction species in this system were ·O2- and h+. This study provided a simple approach to overcoming the limitations of CN in dye wastewater treatment.

Investigation of recombination processes in bulk-heterojunction organic solar cell by extraction of injected charge carriers

In this paper, we used extraction of injected charge carriers technique and time-of-flight method to establish recombination rate dependency on carrier concentration and thickness in a bulk-heterojunction organic solar cell with the active layer blend consisting of poly(3-hexylthiophen-2,5-diyl) and [6,6]-phenyl-C61-butyric acid methyl ester (P3HT: PCBM). Using aforementioned techniques and numerical calculations, we determined that 1.8-diiodiooctane processing additive in combination with chlorobenzene solvent in solution-processed P3HT: PCBM samples causes charge carrier transport and recombination rate changes with increasing device thickness. Also, recombination velocities of P3HT: PCBM blends obtained with the extraction of injected charge carriers technique have a two-component dependency on charge carrier concentration governed by interfacial states between two pure phases.

A facile molecular aggregation of isoquinoline based g-C3N4 for high photocatalytic performance under visible light illumination

Graphitic carbon nitride, g-C3N4 (CN) is regarded as an excellent metal-free semiconductor known for its potential solar fuel generation and pollutant degradation. In this study, a carbon richer substance, (5,8-dibromoisoquinoline (BQ)) was used to feed its catalytic function through conventional copolymerization (molecular doping) process at 550°C under a nitrogen atmosphere. The incorporation of BQ monomer in the triazine oligomers of CN in turn enhanced the specific surface area, thereby, improving the lifespan of photoexcited charge carriers, decreasing the charge recombination rate, energy bandgap, and altering the optoelectronic characteristics of CN. On average, the rate of hydrogen (H2) production over-optimized 10BQ/CN was 710.1 µmol/h much superior and 10 times higher than that of pure CN (71.9 µmol/h). Particularly, the kinetics of the photocatalytic degradation of RhB over 10BQ/CN followed pseudo-order kinetics and the rate constant was three times larger than pure CN. Our results illustrate the crucial importance of conjugated monomers in improving photocatalysis process for future energy demand by providing key steps towards sustainable energy production.

Precise interface modulation cascade enables unidirectional charge transport

Maneuvering spatial photo-induced charge modulation/separation over semiconductor-based photocatalysts represents an enduring challenge in solar-powered photoredox catalysis, but suffers from sluggish charge transport kinetics, confined light absorption scope, limited active species, and rapid charge recombination rate. Herein, we conceptually demonstrate the elaborate design of all transition metal chalcogenides (TMCs)-comprising heterostructures via a facile, controllable, and precise cascade cation exchange strategy. This progressive route strategically extends the light absorption of TMCs, engenders elegant heterostructured interface, and furnishes favorable energy level alignment. The resultant TMCs heterostructures demonstrate markedly enhanced and multifarious photoactivities, owing predominantly to the robust interfacial electronic coupling and applicable energy level configuration among the building blocks, synergistically resulting in the reinforced charge transfer impetus and considerably prolonged charge lifespan. Our work would provide an emerging avenue to fine tuning of vectorial charge motion via such a judicious interface modulation strategy for solar-to-chemical energy conversion.

Combination of MoS2 nanopetals with Ag nanoparticles decorated graphene oxide for boosting photocatalytic abatement of recalcitrant pollutants under visible light irradiation

Herein, various weight ratios (1:1, 1:3, and 3:1) of MoS2/GO composites decorated with Ag nanoparticles (named as MAG) have been prepared by microwave-assisted route. XRD and XPS investigations indicated the catalyst crystallinity and elemental oxidation states. Morphological analysis revealed presence of small MoS2 nanopetals scattered on GO sheets with Ag NPs dispersed on surface whereas BET-analysis disclosed its excellent surface area (∼88 m2/g). Optical properties of MAG catalysts revealed that they were highly visible-light active, with a bandgap of 2.15 eV and a lower charge recombination rate. Excellent efficiency was observed for TC (90.7%; 0.0186 min−1) and FIP-degradation (85.2%; 0.0177 min−1) with 4 mg MAG (3:1) catalyst at neutral pH under visible-light irradiation owing to high synergistic interaction (∼2.21) in the composite. Effects of catalyst amount, pH, and effective area of illumination on degradation were investigated. High reusable nature of the catalyst (65% (TC) and 58% (FIP) efficiency after 5 cycles) was supported by post-photocatalytic characterization studies. Photodegradation products of TC were determined via LC-MS studies. Holes and hydroxyl radicals were majorly involved in degradation process revealed by trapping studies. High COD (70.4%) and TOC (55.1%) removal rates confirm high photo-mineralization of real-wastewater without any pre-treatment. The current investigation, combined with comparative literature, illustrates real-world potential of MAG catalysts for eradication of resistant pollutants.

A DFT+U approach: Superior charge transfer characteristics and optoelectronic properties of GQD@TiO2 rutile (110) surface for improved hydrogen evolution

The understanding on complex electronic structure and charge transfer characteristics is crucial in the development of heterostructure-based photocatalyst such as graphene quantum dots (GQD) and titanium dioxide (TiO2). Simulation studies will be useful in gaining valuable insight on the complex system at atomistic level. Herein, for the first time, a theoretically designed heterogeneous GQD modified TiO2 (110) interface model using Hubbard's modified first-principles density functional theory (DFT+U) is presented. The structural properties were simulated with Perdew–Burke–Ernzerhof assisted generalized gradient approximation (GGA+PBE) and optoelectronic properties with Hubbard's modified (GGA+U) exchange correlation functional. The addition of GQD reduces the bandgap energy of the TiO2 rutile (110) surface from 2.95 eV to 1.86 eV, thereby improving the visible light response as it reduces the electron transition energy. Charge density difference map and Mulliken population analysis demonstrate frequent transfer of charges from GQD to the TiO2 surface, resulting in reduction of charge recombination rate. Moreover, the energy band edge estimation confirms a suitable band edge position in accordance with the redox potential of water. The collective effect of the heightened absorption of visible light and effective charge separation led to a significant photocatalytic performance of the hybrid photocatalyst.

An emerging photocatalyst for wastewater remediation: a mini-review on CaCu3Ti4O12 photocatalysis.

Ceramics-based filter for water treatment is an ancient technology to procure potable water at the household level. The traditional clay pots (vessels or hollow cylindrical container) have been used since long in the developing countries. The ceramic material (CaCu3Ti4O12 or CCTO) is a hetero-junction of titanium oxide, a well-known UV-active photocatalyst, and visible light absorbing CuO materials. This hetero-junction is able to overcome the limitations such as high bandgap, poor stability, low efficiency, and high photo-generated charge (e-/h+) recombination rate, associated with the other commonly used metal oxide semiconductor photocatalysts. Moreover, the low-cost, viable and facile synthesis routes for CCTO triggered its potential applications in photoelectrochemical and photocatalytic processes. This review will elaborate on the available literature demonstrating the visible light activity of CCTO photocatalysts in water treatment technologies. Furthermore, the mechanism of photocatalysis and synthesis routes are presented in this work for broader impact of the CCTO potential applications. The extended porous character and excellent surface texture have made the ceramic materials as an ideal choice to combat the bacteria, pathogens and turbidity in aqueous medium at household level. Specifically, the controlled size and shape make the CaCu3Ti4O12 (CCTO) an excellent visible light-driven photocatalyst, involving highly reactive species such as •OH, •O2- anions, h+, and e-, for the removal of organic and inorganic pollutants from water.

Accelerating the discovery of high-performance donor/acceptor pairs in photovoltaic materials via machine learning and density functional theory

The gigantically unexplored chemical space for the combinations of donor and acceptor poses a mammoth challenge in enhancing power conversion efficiency. Herein, a strategy integrating machine learning and density functional theory was proposed to assist the rational screening of prominent donor/acceptor pairs. Notably, 10 promising donor/acceptor pairs were ultimately sieved out with power conversion efficiency lager than 18.22%. Furthermore, the density functional theory computation expressed that the new donor/acceptor pair of D18/BTP-eC9 possessed stronger absorption intensity, while the KCS/KCR (ratio of charge separation rate and charge recombination rate) and μe (electron mobility) were larger than those of the best known D18/Y6 with the increments of 201.31% and 125.98% respectively. The SHapley Additive exPlanations analysis revealed that the two most important features of A_nR08 and D_D/Dtr12 were positively related to the improvement of power conversion efficiency. It was found that A_nR08 was positively associated with π-conjugation strength, and high D_D/Dtr12 suggested the highly fused chemical structure, indicating the practical clues in discovering top-performing donor/acceptor pairs.

Precisely engineered type II ZnO-CuS based heterostructure: A visible light driven photocatalyst for efficient mineralization of organic dyes

Herein, type-II band alignment of magnetic ZnO/CuS has been achieved by assembling p-type CuS nanoparticles on n-type ZnO heterostructures to accomplish the photocatalytic degradation of two colored cationic dyes, namely, methylene blue (MB) and toluidine blue (TB). The material exhibited excellent photocatalytic efficiency towards MB and TB with 93% and 87.5% degradation in just 16 and 18 min respectively. The efficacy of doped photocatalyst (FSZCS) was found to be 6 times higher than the undoped material (Fe3O4@SiO2@ZnO; FSZ) whereas pristine CuS degraded only 50% of the dye sample under identical conditions. Therefore, the dramatic enhancement of the photocatalytic degradation performance could be attributed to the synergetic effect created by doping CuS over magnetic ZnO nanocomposites which extended the photoresponse of ZnO by driving the entire degradation process under visible light irradiation and also reducing the charge recombination rate. The plausible mechanistic pathway and identification of degradation products was discussed in detail on the basis of scavenger studies as well as GC–MS analysis. Furthermore, the designed catalyst could be recycled and reused up to 5 runs without any significant decrease in its photocatalytic activity. The reported procedure exhibited multiple advances as it proceeded by utilizing renewable household LEDs as power source at room temperature without the use of any additional oxidant under neutral pH conditions thus, paving a strong path towards sustainable, green and responsible chemistry.

Synthesis of bismuth ferrite by sol-gel auto combustion method: Impact of citric acid concentration on its physicochemical properties

In this study, pure phase BiFeO3 was prepared via a facile sol-gel auto-ignition route using water as a solvent. The influence of citric acid to metal nitrates molar ratio on physicochemical properties of BiFeO3 was also investigated through FTIR, XRD, PL, UV, SEM, and BET analysis. The XRD of the prepared samples revealed the rhombohedral perovskite structures belong to space group R3c. In addition, the BFO2:1 sample showed the smallest crystallite size (42 nm) with the highest purity and recombination rate; while the BFO1:2 sample showed the lowest purity and electron charge recombination rate. The surface areas of the BFO1:1, BFO1:2, and BFO2:1 samples were 1.63, 2.13, and 1.84 m2/g, respectively. Moreover, the bandgaps were found to be 2.17, 2.11, and 2.21 eV for the prepared BFO1:1, BFO1:2, and BFO2:1, respectively. In addition, the appearance of a near-IR band around 814 cm−1 confirms the presence of Bi2Fe4O9 byproduct in the BFO1:2 sample. Finally, SEM revealed that BFO2:1 sample was well-distributed and exhibited uniform morphology, referring to citric acid's ability to stabilize and disperse bismuth ferrite NPs. Furthermore, BFO1:2 sample showed enhanced photocatalytic activity in CR dye degradation than BFO1:1 and BFO2:1 samples, attributed by the increase in the surface area and minimized electron-hole recombination. This strategy eliminates the use of conventional organic solvents and provides an effortless and efficient way to prepare pure BiFeO3 and BiFeO3/Bi2Fe4O9 heterojunction nanocomposite that are potentially applicable for photocatalyst and in solar cell production.

Energy Band Engineering by CdTe/Si Codoped TiO2 Nanoarrays for Enhanced Photoelectrochemical Water Splitting

The wide bandgap energy of TiO2 limited its photocatalytic activity to UV light. To meet this challenge, TiO2 nanorods were doped with Si atoms and decorated by CdTe QDs to enhance the electronic structure, broaden the absorption domain, and improve photoelectrochemical (PEC) water splitting. Incorporation of Si atoms in the TiO2 structure effectively enhanced the transfer of charge carriers and the wettability of the surface in the Si:TiO2 electrode and made it an effective platform for solar-assisted water splitting. Moreover, the IPCE results prove that CdTe QDs with high absorption coefficient and photon upconversion spread the photoresponse of CdTe/Si:TiO2 to visible light with an improved photocurrent density of 4.3 mA cm–2 at the potential of 1.23 V vs RHE. The excellent increase of 12.5 times in PEC activity of CdTe/Si:TiO2 electrode as compared to unmodified TiO2 nanoarrays and its low overpotential are due to the faster electron transfer kinetics, enhanced charge carriers density (Nd), and reduced charge recombination rate. The photocurrent stability of CdTe/Si:TiO2 in numerous on/off cycles and its long-term durability with a photocurrent decay of about 5% over 10 h show its high photocorrosion resistance. The current study signifies that CdTe/Si:TiO2 is a suitable and highly efficient photoelectrocatalyst for water splitting.

Quadrupolar Ultrafast Charge Transfer in Diaminoazobenzene-Bridged Perylenediimide Triads.

Strong push-pull interactions between electron donor, diaminoazobenzene (azo), and an electron acceptor, perylenediimide (PDI), entities in the newly synthesized A-D-A type triads (A=electron acceptor and D=electron donor) and the corresponding A-D dyads are shown to reveal wide-band absorption covering the entire visible spectrum. Electrochemical studies revealed the facile reduction of PDI and relatively easier oxidation of diaminoazobenzene in the dyads and triads. Charge transfer reversal using fluorescence-spectroelectrochemistry wherein the PDI fluorescence recovery upon one-electron oxidation, deterring the charge-transfer interactions, was possible to accomplish. The charge transfer state density difference and the frontier orbitals from the DFT calculations established the electron-deficient PDI to be an electron acceptor and diaminoazobenzene to be an electron donor resulting in energetically closely positioned PDIδ- -Azoδ+ -PDIδ- quadrupolar charge-transfer states in the case of triads and Azoδ+ -PDIδ- dipolar charge-transfer states in the case of dyads. Subsequent femtosecond transient absorption spectral studies unequivocally proved the occurrence of excited-state charge transfer in these dyads and triads in benzonitrile wherein the calculated forward charge transfer rate constants, kf , were limited to instrument response factor, meaning >1012 s-1 revealing the occurrence of ultrafast photo-events. The charge recombination rate constant, kr , was found to depend on the type of donor-acceptor conjugates, that is, it was possible to establish faster kr in the case of triads (∼1011 s-1 ) compared to dyads (∼1010 s-1 ). Modulating both ground and excited-state properties of PDI with the help of strong quadrupolar and dipolar charge transfer and witnessing ultrafast charge transfer events in the studied triads and dyads is borne out from the present study.

Simultaneous doping of sulfur and chloride ions into ZnO nanorods for improved photocatalytic properties towards degradation of methylene blue

In this study, we have successfully doped sulfide (S−2) and chloride (Cl−1) simultaneously into ZnO by hydrothermal method. The structure, morphology, composition, and optical properties of the prepared S–Cl doped ZnO nanostructures were investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), scanning transmission electron microcopy (STEM), energy dispersive spectroscopy (EDX) and UV–visible (UV–Vis) spectroscopy techniques. After, doping of both S and Cl into ZnO no significant alteration in the nanorod morphology was noticed. The wurtzite crystal structure of ZnO was retained with a red shift in the 2Ɵ towards high angle. The XRD results are supported by the high-resolution transmission electron microscopy. The elemental analysis revealed a successful doping of S and Cl into ZnO structure. Importantly, the optical band gap of ZnO was decreased 2.9 eV upon doping of S and Cl ions. Thus, the nonmetal doping via S and Cl has significantly enhanced the photocatalytic properties of ZnO towards methylene blue (MB) due to high density of active sites and decreased charge recombination rate of electron-hole pairs. The photo-degradation efficiency towards MB reached 99.64% upon using S and Cl doped ZnO photocatalyst using optimum dose of 15 mg and initial dye concentration of 1.87 × 10−6 M. The use of simultaneous nonmetal doping concept could of great importance for the preparation of other nanostructured materials and their use in potential applications like solar cells, and photoelectrochemical water splitting.

Insight into the Roles of Metal Loading on CO2 Photocatalytic Reduction Behaviors of TiO2.

The photocatalytic reduction of carbon dioxide (CO2) into value-added chemicals is considered to be a green and sustainable technology, and has recently gained considerable research interest. In this work, titanium dioxide (TiO2) supported Pt, Pd, Ni, and Cu catalysts were synthesized by photodeposition. The formation of various metal species on an anatase TiO2 surface, after ultraviolet (UV) light irradiation, was investigated insightfully by the X-ray absorption near edge structure (XANES) technique. CO2 reduction under UV-light irradiation at an ambient pressure was demonstrated. To gain an insight into the charge recombination rate during reduction, the catalysts were carefully investigated by the intensity modulated photocurrent spectroscopy (IMPS) and photoluminescence spectroscopy (PL). The catalytic behaviors of the catalysts were investigated by density functional theory using the self-consistent Hubbard U-correction (DFT+U) approach. In addition, Mott–Schottky measurement was employed to study the effect of energy band alignment of metal-semiconductor on CO2 photoreduction. Heterojunction formed at Pt-, Pd-, Ni-, and Cu-TiO2 interface has crucial roles on the charge recombination and the catalytic behaviors. Furthermore, it was found that Pt-TiO2 provides the highest methanol yield of 17.85 µmol/gcat/h, and CO as a minor product. According to the IMPS data, Pt-TiO2 has the best charge transfer ability, with the mean electron transit time of 4.513 µs. We believe that this extensive study on the junction between TiO2 could provide a profound understanding of catalytic behaviors, which will pave the way for rational designs of novel catalysts with improved photocatalytic performance for CO2 reduction.

Symmetry-Breaking Charge Separation in Molecular Constructs for Efficient Light Energy Conversion

The generation of electron–hole radical pair at the active layer of organic photovoltaics through symmetry-breaking charge separation (SB-CS) has a crucial role in enhancing open-circuit voltage (Voc) and thereby increasing power conversion efficiency. Since the SB-CS materials achieve intramolecular charge separation with a negligible energetic driving force and decelerated charge recombination (CR) rate, SB-CS has been subjected to extensive experimental and theoretical studies. This Focus Review assesses the fundamentals of photosynthetic reaction centers, especially the “special pair”, and discusses how covalent control over the geometric arrangement, surrounding dielectric medium, and substitutions on multichromophoric perylenediimide architecture affects the energy landscape of SB-CS and CR. We systematically summarize the kinetically favored undesirable radiative and non-radiative deactivation channels of SB-CS and CR processes on diverse chromophoric arrangements. Here, we suggest new rational design principles to fine-tune the electron-transfer dynamics at the molecular level to improve the performance of light–energy conversion devices.

Dual Passivation of Point Defects at Perovskite Grain Boundaries with Ammonium Salts Greatly Inhibits Nonradiative Charge Recombination.

Experiments demonstrate that grain boundaries (GBs) exhibit detrimental effect on carrier lifetimes in MAPbI3 (MA= CH3NH3+). On the basis of the nonadiabatic (NA) molecular dynamics simulations, we demonstrated that NH4Cl can simultaneously passivate the common point defects that introduce recombination centers at GBs and accelerate electron-hole recombination but shows small effects in the bulk. The MA interstitial (MAi) and the substitutional MA to Pb (MAPb) in pristine MAPbI3 leave the band gap and charge recombination rates largely unchanged but create deep electron traps at GBs by separately either distorting inorganic octahedra or creating an I-dimer. Cl- and NH4+ remove the in-gap states by either restoring the distorted octahedra or destroying the I-dimer. Thus, the band gap recovers to the pristine system, NA coupling decreases, and decoherence accelerates, extending the carrier lifetime even twice longer than MAPbI3. This study shows that the negative role of GBs can be removed by dually passivating with NH4Cl.

Nanoarchitectonics of uniformly distributed noble-metal-free CoP in g-C3N4 via in-situ fabrication for enhanced photocatalytic and electrocatalytic hydrogen production

Developing an efficient, robust and low-budget bifunctional material for hydrogen evolution is a daunting challenge, which has attracted plenty of researchers’ interest. Herein, we report the non-noble metal bifunctional g-C3N4/CN/CoP catalysts in situ formed for both photocatalytic and electrocatalytic hydrogen production through a convenient phosphorization process. It was found that the optimal g-C3N4(90)/CN300/CoP3 composite not only had the best photocatalytic hydrogen production rate (29.78 mmol·g−1·h−1) in the dye sensitization system, but also had an excellent electrocatalytic hydrogen evolution activity, with an overpotential of 221 mV at 10 mA·cm−2. The XRD, FT-IR, TG, et al. confirm the close contact between ZIF-Co and g-C3N4 in the ideal g-C3N4/ZIF-Co precursor could expediently achieve the uniformly distributed CoP to accelerate electron transfer and reduce the recombination rate of charge. This work can provide a novel strategy to fabricate non-noble metal dual-functional materials for photocatalytic and electrocatalytic hydrogen production to solve energy crises and environmental further.

Persistent radical cation sp2 carbon-covalent organic framework for photocatalytic oxidative organic transformations

Persistent radical covalent organic frameworks (COFs) have exhibited great application potential in the fields of photocatalysis, magnetism, and biology. However, there is still a lack of a simple, green, and effective way to produce persistent radical COFs. Here, we synthesized two sp2 carbon-covalent organic frameworks (sp2C-COFs) with persistent triphenylamine radical cation (TPA+•), which can be generated by simple light irradiation since the effective donor–acceptor heterojunction is formed in ordered skeleton. The number of persistent TPA+• will increase with the intensity of light irradiation and the photogenerated electrons generated simultaneously can be consumed by O2 to form reactive oxygen species, which can be then used to carry out the oxidative organic transformations under visible light. In addition, femtosecond-transient absorption spectra prove that the difference in the structure of the two radical cation sp2C-COFs will significantly influence the charge recombination rate, so that the materials show different catalytic efficiency.