Matched Band Gap Research Articles

Effect of Anion-Directed Structural Tuning of Triazole-Containing Ag(I) Coordination Polymers for "Turn-on" Sensing of the Disulfide (-S-S-) Amino Acid over the Monosulfide (-SH) Form: Experiments and DFT Corroboration.

Identification of disulfide-peptide-bond-containing glutathione (GSSG) over the monosulfide form (GSH) remains a very challenging task because of their identical chemical properties. Although GSH detection has been well documented, selective detection of GSSG has rarely been reported. Here, four cationic Ag-based coordination polymers (Ag CPs) were synthesized using newly synthesized monotriazole linker 3-amino-5-(4H-1,2,4-triazol-4-yl)pyridine to selectively screen GSSG over GSH. The judicious choice of the counteranion in the metal salt changes the architecture, which affects the detection limit at the parts per million level. The restriction of the photoinduced electron transfer process is the driving reason for the enhancement of the fluorescence, owing to the favorable energy band gap match of the Ag CPs with GSSG over GSH. The de novo strategy for incorporating polar heteroatoms (N) into the CP network plays a pivotal role in the host-guest noncovalent interactions with donor-acceptor transfer of electrons, which was supported by X-ray photoelectron spectroscopy and density functional theory studies. The Ag CPs are thermochemically robust, recyclable, and work efficiently in a very short time (within ∼14-18 s) in different pH ranges. Additionally, detection of GSSG in serum samples was carried out with appreciable detection limits and recovery percentages (94.40-117.89%).

Highly efficient narrow bandgap Cu(In,Ga)Se2 solar cells with enhanced open circuit voltage for tandem application

Although an ideal bandgap matching with 0.96 eV and 1.62 eV for a double-junction tandem is hard to realize practically, among all mature photovoltaic systems, Cu(In,Ga)Se2 (CIGSe) can provide the closest bandgap of 1.00 eV for the bottom sub-cell by adjusting its composition. However, pure CuInSe2 (CISe) solar cell suffers strong interfacial carrier recombination. We hereby present approaches to introduce appropriate Ga gradients in both the back and front parts of absorber while maintaining the absorption spectrum close to CISe. With an appropriate front Ga gradient, the open circuit voltage can be enhanced by ~30 mV. With a pre-deposited CIGSe layer and a high copper excess deposition during absorber growth, the Ga diffusion can be well suppressed and a wide U-shaped Ga grading with a minimum bandgap of 1.01 eV has been created. Our optimized narrow-bandgap CIGSe solar cell has achieved a certified record PCE of 20.26%, with a record-low open circuit voltage deficit of 368 mV and a record-high contribution of 10% absolute efficiency to a four-terminal tandem. This work demonstrates the potential of controlling gallium diffusion to improve the performance of narrow bandgap CIGSe solar cells for tandem applications.

Flexible Perovskite Solar Cells: A Futuristic IoTs Powering Solar Cell Technology, Short Review.

The perovskite solar cells (PSCs) technology translated on flexible substrates is in high demand as an alternative powering solution to the Internet of Things (IOTs). An efficiency of ∼26.1% on rigid and ∼25.09% on flexible substrates has been achieved for the PSCs. Further, it is also reported that F-PSC modules have a surface area of ∼900 cm2, with a PCE of ∼16.43%. This performance is a world record for an F-PSC device more significant than ∼100 cm2. The process optimization, and use of new transport materials, interface, and compositional engineering, as well as passivation, have helped in achieving such kind of performance of F-PSCs. Hence, the review focuses mainly on the progress of F-PSCs and the low-temperature fabrication methods for perovskite films concerning their full coverage, morphological uniformity, and better crystallinity. The transmittance, band gap matching, carrier mobility, and ease of low-temperature processing are the key figures of merit of interface layers. Electrode material's flexible and transparent nature has enhanced the device's mechanical stability. Stability, flexibility, and scalable F-PSC fabrication challenges are also addressed. Finally, an outlook on F-PSC applications for their commercialization based on cost will also be discussed in detail.

Unravelling Structural, Optical, and Band Alignment Properties of Mixed Pb-Sn Metal-Halide Quasi-2D Ruddlesden-Popper Perovskites.

Lead-tin (Pb-Sn) mixed-halide perovskites show potential for single-junction and tandem solar cells due to their adjustable band gaps, flexible composition, and superior environmental stability compared to three-dimensional (3D) perovskites. However, they have lower power conversion efficiencies. Understanding band alignment and charge carrier dynamics is essential for enhancing photovoltaic performance. In this view, herein we have prepared thin films of mixed Pb-Sn-based two dimensional (2D) Ruddlesden-Popper (RP) perovskites BA2FA(Pb1-xSnx)2I7 using a solution-based method. XRD study revealed the formation of orthorhombic phases for pristine (BA2FAPb2I7) and mixed Pb-Sn perovskite thin films. UV-vis analysis showed that different n = 2 and n = 3 phases are present in the pristine sample. In contrast, Pb-Sn-doped samples showed no signature of other phases with a prominent red-shift in the visible spectral region. Cyclic voltammetry showed peaks for electron transfers at the band edges. Additionally, electrochemical and optical band gap matching was observed, along with decreased peak intensity due to less reactant and altered electrolyte-perovskite interface stability. Density functional theory (DFT) calculations revealed that the reduced band gap is due to the alteration of electrostatic interactions and charge distribution within the lattice upon Sn substitution. Low-temperature PL analysis provided insights into charge carrier dynamics with Sn substitution and suggested the suppression of higher n phases and self-trapped excitons/carriers in mixed Pb-Sn quasi-2D RP perovskite thin films. This study sheds light on the electron transfer phenomena between TiO2 and SnO2 layers by estimating band offsets from valence band maximum (VBM) and conduction band minimum (CBM), which is crucial for future applications in fabricating stable and efficient 2D-Pb-Sn mixed perovskites for optoelectronic applications.

Effects of subcell bandgap matching on the performance of perovskite/Cu(In,Ga)Se2 tandem solar cells

The tandem solar cell is composed of a wide bandgap top subcell and a narrow bandgap bottom subcell, which is a promising technology to surpass the theoretical efficiency of single-junction solar cell. Since the currents are generated by photo-generated carriers and the two subcells are united in series, the absorber thickness should be adjusted with the change of the bandgaps to ensure that the two subcells have the same currents. In this study, the impacts of subcell bandgaps on perovskite/Cu(In,Ga)Se2 tandem solar cells were investigated using SCAPS-1D. For perovskite top subcells, the short-circuit current and power conversion efficiency increased with the absorber thickness increasing, and photons in short-wavelength part could be absorbed by perovskite solar cells, while photons in long-wavelength part were almost not absorbed. In tandem solar cells, the increasing bandgap of top subcell and the decreasing bandgap of bottom subcell required higher top subcell thickness to achieve the current matching condition. The top subcell bandgap needed to be wide enough and the bottom subcell bandgap needed to be narrow enough to get the same current. The efficiency increased as the top subcell bandgap increased to 1.7 eV, and started to decline with the further increase of bandgap. Moreover, the efficiency increased as the bottom subcell bandgap increased up to 1.28 eV, but decreased when the bandgap kept increasing. The optimized tandem solar cell achieved the highest efficiency of 32.71 % with the top subcell bandgap of 1.7 eV and the bottom subcell bandgap of 1.28 eV.

Investigating the preparation process of excellent Cu3VSe4 absorption layer prepared by amine-thiol system

Cu3VSe4 material has become a new kind of photovoltaic absorber due to its optical bandgap matching light-absorbing, abundant elements in crust, and high light absorption coefficient. Here, we prepared Cu3VSe4 thin films by amine-thiol method and investigated the preparation process of excellent Cu3VSe4 absorption layer for the first time. The effects of various Cu/V ratios on the morphology, structure, and electrical properties of the films are studied. XRD and Raman results show that pure-phase Cu3VSe4 films are obtained with the Cu/V ratios lower than 2.9. SEM results simply adjusting the Cu/V ratio cannot obtain a compact selenized Cu3VSe4 thin films. The best crystallinity of thin film with 2.8 of Cu/V ratio is named as Cu2.8VSe4 and selected as the representative. Though optimizing the selenization conditions, a dense morphology and good electrical properties of the absorption layer can be prepared under 570 °C of the high-temperature process. Our findings can lay the favorable foundation for high-efficiency Cu3VSe4 devices.

Graphdiyne (g-CnH2n-2) nanosheets encapsulated Cu-Co Prussian blue Analogues formed double S-scheme heterojunction for wide spectrum photocatalytic H2 evolution

The frontier of sustainable energy research includes the advancement and creation of stable and efficient photocatalysts for the process of photocatalytic hydrogen evolution (PHE). Graphdiyne (GDY), an innovative carbon allotrope, demonstrates a narrow band gap and exceptional photogenerated charge mobility, making it extremely promising in the field of photocatalysis. In addition, Prussian Blue Analogues (PBA) are a unique category of metal–organic frameworks (MOFs) with open framework structures and strong stability. Compounds formed by ligands and various metal ions in PBA materials exhibit excellent performance. This work primarily enhances wide spectrum PHE by in situ growing GDY nanosheets onto Cu-Co PBA to construct a double S-scheme Cu-Co PBA@GDY/CuI (CCGC) heterojunction. The amorphous GDY can provide abundant active sites for photocatalytic hydrogen evolution reaction. Furthermore, the nanosheet properties of GDY were confirmed using Atomic Force Microscopy (AFM). The highest PHE rate of Cu-Co PBA@GDY/CuI-10 (CCGC-10) reaches 12947.8 μmol h−1 g−1 with a apparent quantum efficiency (AQE) of is 4.37 % at 520 nm, and exhibits good cycling stability. Based on the bandgap matching theory, the spatial behavior of photogenerated carriers in GDY, CuI, and Cu-Co PBA was effectively controlled, resulting in a close interface with a double S-scheme heterojunction charge transfer in Cu-Co PBA@GDY/CuI. The S-scheme photogenerated charge transfer pathway in CCGC was further confirmed through in-situ XPS, electron spin resonance (ESR) and work function (Wf). This work proposes a novel approach for the synthesis of solar energy conversion composite photocatalysts based on GDY and PBA.

Spectrum splitting approach based design simulation for multilayer chalcogenide solar cell architecture

We report design simulation on multilayer solar cell architecture aimed at enhancing the absorption efficiency in antimony sulfide (Sb2S3) absorber based cell via spectrum splitting approach. The poor experimental efficiency chalcogenide absorber (say; ∼8% for Sb2S3) based solar cell has been attributed to inadequate rear contact barrier, a high concentration of point defects (both acceptor and donor) within the bulk, low carrier lifetime, and the presence of defects at the absorber/buffer interface. A hetero-structure design modification vis-à-vis experimental report using bandgap tunability of Sb2S3 via point-focusing spectral splitting technique approach has been implemented to upscale the efficiency. The incident solar spectrum has been split into three well defined regimes for a focussed bandgap matching to enable light absorption and minimize transmission and thermalization losses. The adopted point-focusing spectral splitting technique in this work has resulted in an efficiency of 18.0%, which is an advancement by 2.25 times over the highest reported efficiency of 8.0% in the literature for Sb2S3 absorber based solar cells.

Co-evaporated oriented DMA1-xCsxPbI3 perovskite films for photovoltaics

Thermally evaporated cesium lead triiodide (CsPbI3) is a frontier research direction for perovskite-silicon tandem solar cells because of the matching bandgap and good conformality with textured silicon. However, the random orientation and small grains for the co-evaporated CsPbI3 thin films fabricated at low temperature, resulting in harmful defects and non-radiative recombination. Here, dimethylammonium iodide (DMAI) is introduced into the co-evaporation system at a substrate temperature of 50 °C to prepare preferentially oriented DMA0.06Cs0.94PbI3 film with less defects and enhanced humidity stability. The bandgap also can be reduced from 1.76 eV (γ-CsPbI3) to 1.73 eV. The p-i-n photovoltaic device based on this film achieves an efficiency of 16.10% with suppressed non-radiative recombination, rivaling with the thermally evaporated wide-bandgap CsPbI3 solar cells prepared at a high temperature (∼ 350 °C). This in-situ evaporated alloying strategy can pave the way for the crystallization and defect control during perovskite co-evaporation.

Rational design an oval heterostructure and tight linking interface of ZnS@CdS(3) for sensitively photoelectrochemical bioanalysis of PSA

Photoactive material with heterostructures could be effectively employed to promote the photoelectrochemical (PEC) property. Herein, two species heterostructured ZnS@CdS(1−2) composites derived from ZIF-8-S MOFs via a sulfofication reaction in situ using Cd(NO3)2, CdC12 cadmium reagents, and further gained the oval ZnS@CdS(3) after annealing the ZnS@CdS(2). Under irradiation, the PEC results showed that the photocurrent response of ZnS@CdS(3) signally enhanced compared to disordered heterostructures of ZnS@CdS(1), ZnS@CdS(2) and pure ZnS or CdS. It was ascribed to the staggered levels based on matching band-gap to form type II heterojunction of ZnS@CdS(3) could facilitate photo-induced electron/hole (e-/h+) separation and transfer. The obtained photoelectric material with a tight connecting interface also could reduce the carriers transport distance. Besides, the structured and well-distributed ZnS@CdS(3) was beneficial to improve synergistic effect on every component, which resulting in violently photocurrent output. This ZnS@CdS(3) modified ITO electrode to create the PEC biosensor (BSA/anti-PSA/ZnS@CdS(3)/ITO) had been successfully applied for the PSA detection with a wide linear range of 0.001 ∼ 150 ng mL−1 and ultralow detection limit of 0.27 pg mL−1. This research innovatively designed a close contact heterojunction interface with superior PEC nature for biosensor preparations.

A hair-ball heterostructure of MnS-MnS2/CdS with compact linking interface for ultrasensitive photoelectrochemical bioanalysis of carcinoembryonic antigen

The heterostructured photoelectric material is supposed to markedly promote the photoelectrochemical (PEC) property. Herein, the species heterostructured MnS/CdS and MnS-MnS2/CdS(1∼2) composites derived from Mn-ZIF MOFs via a sulfofication reaction using Cd(NO3)2, CdC12 cadmium source, respectively. Under irradiation, the PEC tests showed that the photocurrent response of MnS-MnS2/CdS(1∼2) signally enhanced compared to globose MnS/CdS heterostructure and pure MnS or CdS. It was ascribed to the matching band-gap to form type II heterojunction in MnS-MnS2/CdS(1∼2) which dramatically facilitated photo-induced electron/hole (e−/h+) separation and transfer. The hair-ball morphologies structure of MnS-MnS2/CdS(1∼2) with large number of pores was beneficial to improve penetrating efficiency of the electrolyte liquid. Meanwhile, the well-synergistic effect on the MnS, MnS2, CdS components and with tight connecting heterojunction interface among MnS-MnS2/CdS(1∼2) which also led to violently photocurrent output. Besides, the chitosan (CS) was covalently coupled with glutaraldehyde (GLD) to obtain steady composite film, and the cross-linker of GLD can achieve the high efficiency to graft the Apt-CEA (aptamer) biomolecules, which resulting in the promotion of hybridization reaction efficiency of the CEA target. Hence, this created biosensor of Apt-CEA/GLD-CS/MnS-MnS2/CdS(1)/ITO for the CEA detection displayed a wide linear range from 0.001 to 18 ng mL−1 and with ultralow detection limit of 0.313 pg mL−1. This research innovatively prepared a contact heterojunction interface with special porosities structure, which had superior PEC nature for the fabrication of high-performance biosensor.

Constructing S-scheme heterojunctions through electrostatic self-assembly of Co3O4 quantum dots and CuBr for photocatalytic hydrogen evolution

Utilizing solar energy to power semiconductors for water splitting and hydrogen production is an effective method for clean energy generation. This study presents a new S-scheme heterojunction catalyst, constructed via electrostatic self-assembly of CuBr and Co3O4 quantum dots. The band gap-matching positions and energy band structures of CuBr and Co3O4 quantum dots are well-suited for this purpose. The hydrogen precipitation performance of the resulting CQCB2 catalyst is approximately four times higher than that of a single catalyst. Additionally, CQCB2 exhibits good stability, with an 80% hydrogen precipitation efficiency after four consecutive cycles. The study demonstrates that CQCB2 exhibits a high absorbance intensity, efficient charge separation, low electron transport resistance, and low photogenerated carrier recombination rate. This is further validated by XPS and UPS experiments, which support the S-scheme heterojunction charge transfer mechanism. Overall, this paper provides a unique insight into the study of S-scheme heterojunction catalysts.

Double shelled titanium dioxide@mesoporous organosilica nanotube as an amphiphilic photoactive nanoreactor for efficient photocatalytic oxidation of styrene

In this work, we have proposed a strategy to fabricate double-shell nanotubes as amphiphilic photoactive nanoreactors (HTTBPC) through the ordered hybridization of mesoporous organosilicon (PMO) and titanium dioxide (TiO2) nanotubes. Unlike the previous rough composite, the heterogeneous structure established between cobalt-porphyrin functionalized PMO and conventional TiO2 has a staggered matching band gap, which makes it have excellent light harvesting and high carrier separation ability. This is still unexplored. Interestingly, the prepared photocatalysts exhibited superior activity (99%) and benzaldehyde selectivity (94%) in the oxidation of styrene in water at room temperature, which was 3.8 and 2.8 times higher than that of TiO2 nanotubes and PMO functionalized with cobalt porphyrin, respectively. It was demonstrated that the strong interaction between cobalt porphyrin PMO and TiO2 improved the separation of photogenerated carriers and the amphiphilic properties of mesoporous organosilica boosted the adsorption of substrate molecules in water, contributing to the significantly enhanced photocatalytic activity. This work provides a design of high-performance photocatalysts for alkene oxidation under green conditions.

Efficient Monolithic Perovskite/Silicon Tandem Photovoltaics

Tunable bandgaps make halide perovskites promising candidates for developing tandem solar cells (TSCs), a strategy to break the radiative limit of 33.7% for single‐junction solar cells. Combining perovskites with market‐dominant crystalline silicon (c‐Si) is particularly attractive; simple estimates based on the bandgap matching indicate that the efficiency limit in such tandem device is as high as 46%. However, state‐of‐the‐art perovskite/c‐Si TSCs only achieve an efficiency of ~32.5%, implying significant challenges and also rich opportunities. In this review, we start with the operating mechanism and efficiency limit of TSCs, followed by systematical discussions on wide‐bandgap perovskite front cells, interface selective contacts, and electrical interconnection layer, as well as photon management for highly efficient perovskite/c‐Si TSCs. We highlight the challenges in this field and provide our understanding of future research directions toward highly efficient and stable large‐scale wide‐bandgap perovskite front cells for the commercialization of perovskite/c‐Si TSCs.

Efficient photocatalytic H2 production of g-C3N4 using nickel (II) functional complex as promoter

With the increasingly prominent energy and environmental problems, the construction of sustainable development, green environmental protection and new efficient energy system has become the focus of the world's attention. Photocatalytic hydrogen production technology is an important way to solve energy and environmental problems. The key to realizing the visible light catalytic water hydrogen production technology effectively lies in the selection of photocatalytic materials, graphite phase carbon nitride (g-C3N4) is an important photocatalyst. However, the photocatalytic performance of g-C3N4 is severely limited by the high recombination rate of photogenerated electron-hole pairs. Functional complex has a matching band gap with carbon nitride to form heterojunction structure, which can effectively reduce the photogenic carrier recombination and improve the catalytic hydrogen production performance. For this reason, the functional complex [Ni2(Medpq)2(BPDA)·2H2O] (BPDA = 4,4′-Biphthalic Anhydride, Medpq = 2-methyldipyrido[3,2-f:2′,3′-h]quinoxaline) was synthesized by a hydrothermal process. The matching band gap between [Ni2(Medpq)2(BPDA)·2H2O] and g-C3N4 forms heterojunction structure, which effectively solve the defect of low utilization rate of light energy and improve the catalytic hydrogen production performance of g-C3N4. The experiment proved that complex/g-C3N4 photocatalytic rates of hydrogen production 2054.13 μmol·h−1·g−1, about 5.04 times that of pure g-C3N4 (407.56 μmol·h−1·g−1), thus high-performance of the hydrogen production from water decomposition was realized.

Preparation of S- scheme heterojunction Bi28O32 (SO4)10/NiAl LDH for efficient photocatalytic degradation of tetracycline

At present, the construction of high-efficiency photocatalytic degradation system of antibiotic pollutants has become a research hotspot. In this paper, Bi28O32(SO4)10/NiAl LDH photocatalyst with three-dimensional spherical morphology was successfully prepared by hydrothermal method followed by calcination, thus applying to the degradation of tetracycline. The characterization and photochemical analysis of the resulted material were used to determine the type of formed heterojunction. Bi28O32(SO4)10 and NiAl LDH build a close contact interface. The matching band gap structure makes S-scheme heterojunction formed between the two single component. Benefited from this structure, the Bi28O32(SO4)10/NiAl LDH composite with the mass ratio of 1:1 exhibited 95% efficiency in degradation of tetracycline after irradiation for 120 min, and it is stable, reusable and universal. The apparent rate constant of TC degradation by heterojunction catalyst is greatly increased, which is 5.35 and 4.91 times that of Bi28O32(SO4)10 and NiAl LDH. Overall, this paper provides a way of thinking for the design of new bismuth based photocatalytic materials, and thus providing a reference for the rational design of S-scheme heterojunction.

Enhanced triboelectric degradation of organics by regulating oxygen vacancies and constructing heterojunctions

In contrast to conventional oxidation techniques, tribocatalysis degradation of organics has gained much attention in recent years due to its mild requirement and low amount of energy needed. Therefore, we prepared Ba1.4Sr3.6NdNb7Ti3O30 (BSNNT) ferroelectric nanopowder by a solid-phase synthesis method and further investigated the effects of oxygen vacancies and heterojunctions on the tribocatalysis effect. The results showed that the introduction of oxygen vacancies not only reduced the valence electron potential required for the reaction but also greatly reduced the combination of electrons and holes. The efficiency of degradation of RhB by oxygen vacancy-rich BSNNT can reach 97 % after 2 h. Furthermore, the BSNNT-N2/CN-2 (BN2/CN-2) Z-type heterojunction achieves a tribocatalytic enhancement with 98.2 % RhB degradation in 2 h, which is attributed to the built-in electric field of ferroelectric materials and the appropriate band gap matching between g-C3N4 (CN) and BSNNT-N2 (BN2), facilitating the electron and hole transport paths between the semiconductor and ferroelectric materials. Therefore, new approaches to enhance tribocatalytic degradation of dye wastewater by increasing oxygen vacancies and constructing heterojunctions were proposed and examined based on tungsten bronze ferroelectric materials.

BiPO4/Ov-BiOBr High-Low Junctions for Efficient Visible Light Photocatalytic Performance for Tetracycline Degradation and H2O2 Production

Through a two-step solvothermal method, different molar ratios of BiPO4 were grown in situ on the surface of oxygen-vacancy-rich BiOBr (Ov-BiOBr), successfully constructing a BiPO4/Ov-BiOBr heterojunction composite material. By constructing a novel type I high-low junction between the semiconductor BiPO4 and Ov-BiOBr, stronger oxidative holes or reductive electrons were retained, thereby improving the redox performance of the photocatalyst. The composite catalyst with a 10% molar content of BiPO4 demonstrated the highest degradation rate of tetracycline (TC), degrading over 95% within 90 min, with a rate constant of 0.02534 min−1, which is 2.3 times that of Ov-BiOBr and 22 times that of BiPO4. The 10% BiPO4/Ov-BiOBr sample displayed the best photocatalytic activity, producing 139 μmol·L−1 H2O2 in 120 min, which is 3.6 times the efficiency of Ov-BiOBr and 19 times that of BiPO4. This was due to the appropriate bandgap matching between BiPO4 and Ov-BiOBr, the photo-generated electron transfer channel via Bi-bridge, and efficient charge separation. It was inferred that the free radical species ·OH and ·O2− played the dominant role in the photocatalytic process. Based on experimental and theoretical results, a possible photocatalytic mechanism was proposed.

Cu2O/2D COFs Core/Shell Nanocubes with Antiphotocorrosion Ability for Efficient Photocatalytic Hydrogen Evolution.

Photocorrosion of highly active photocatalysts is an urgent problem to be solved in the field of photocatalysis; however, searching for effective strategies for inhibiting photocorrosion of photocatalysts is still a grand challenge. Herein, we design and construct a class of Cu2O/2D PyTTA-TPA COFs (PyTTA: 1,3,6,8-Tetrakis(4-aminophenyl)pyrene, TPA: p-benzaldehyde) core/shell nanocubes to greatly boost the performance of photocatalytic hydrogen evolution and significantly inhibit the photocorrosion. The optimal Cu2O/PyTTA-TPA COFs core/shell nanocubes exhibit an excellent photocatalytic H2 evolution rate of 12.5 mmol h-1 g-1, which is ∼8.0-fold and ∼20.0-fold higher than those of PyTTA-TPA COFs and Cu2O nanocube, respectively, and also is the best in all the reported metal oxides catalytic materials. The mechanism studies demonstrate that the appropriate matching band gaps and tight integration of PyTTA-TPA COFs and Cu2O nanocubes can significantly facilitate the separation of photogenerated electron-hole pairs in the Cu2O/PyTTA-TPA COFs core/shell nanocube during the photocatalytic process, which ameliorates the photocatalytic H2 evolution activity. Most importantly, the 2D PyTTA-TPA COFs shell with outstanding intrinsic stability protects Cu2O nanocubes core from photocorrosion by showing no morphology and crystal structure change after 1000 times of photoexcitation.

Biosensor with enhanced photoelectrochemical activity based on heterogeneous Co3O4@C/TiO2 composite with efficient photogenerated carrier separation for chlorpyrifos detection

Photoactive materials with heterostructures are highly effective for photoelectrochemical (PEC) detection. In this study, a honeycombed Co3O4@C was fabricated by calcining the metal-matrix complex of Co(NO3)2/Mel (melamine). Thereafter, the photoactive TiO2 particles were coupled with Co3O4@C to obtain a heterogeneous Co3O4@C/TiO2 composite based on matching band gaps. Under visible-light illumination, the Co3O4@C/TiO2/ITO modified electrode exhibited superior PEC response compared with Co3O4@C/ITO and TiO2/ITO electrodes. The enhanced PEC response can be attributed to the honeycombed and thin-shelled Co3O4@C, which boosted the visible-light harvesting capacity. Meanwhile, the high porosity on Co3O4@C facilitated infiltration to the electrolyte and increased the electronic transportation efficiency. The p–n-type heterojunction interface between the Co3O4@C and TiO2 enhanced the migration of the photo-induced e−/h+ pair by preventing their recombination. Furthermore, acetylcholine esterase (AChE) was assembled on the chitosan (CS)/glutaraldehyde (GLD)–modified Co3O4@C/TiO2/ITO electrode surface to realize a PEC sensing platform (AChE/CS-GLD/Co3O4@C/TiO2/ITO). Acetylcholine chloride (ATCl) was hydrolyzed using AChE to produce a thiocholine biomolecule, which behaved as an electron donor and generated a photocurrent signal. However, when the bio-recognition component of AChE was suppressed by chlorpyrifos, the reduced production of thiocholine weakened the photocurrent output. Under optimal conditions, proposed sensor is effective for testing chlorpyrifos owing to its high sensitivity. The sensor has a wide linear range of 0.0001–225 µg mL−1 and a low detection limit (2.9×10−5 µg mL−1). The sensing platform also has high specificity, reproducibility, and stability. This study developed a photoactive material using a p-n–type heterojunction for application to the development of efficient sensors.