Photocurrent Action Spectra Research Articles

Rhombohedral boron monosulfide as a metal-free photocatalyst

Most of previous photocatalysts contain metal species, thus exploring a metal-free photocatalyst is still challenging. A metal-free photocatalyst has an advantage for the development of economical and non-toxic artificial photosynthesis system and/or environmental purification applications. In this study, rhombohedral boron monosulfide (r-BS) was synthesized by a high-pressure solid-state reaction, and its photocatalytic properties were investigated. r-BS absorbed visible light, and its photocurrent action spectrum also exhibited visible light responsivity. The r-BS evolved hydrogen (H2) from water under ultraviolet (UV) as well as under visible light irradiation, and its internal quantum efficiency reached 1.8% under UV light irradiation. In addition to the H2 evolution reaction, the r-BS photocatalyst drove carbon dioxide (CO2) reduction and dye oxidation reactions under UV irradiation. Although bare r-BS was not so stable under strong light irradiation in water, cocatalyst modification improved its stability. These results indicate that r-BS is a new class of non-metal photocatalyst applicable for H2 production, CO2 reduction, and environmental purification reactions.

Excitation-Wavelength-Dependent Charge Injection and Hole Localization in Diblock Oligomers Anchored to TiO2.

A series of diblock oligomers containing oligothiophene (Tn, n = 4, 5) and 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadizole (TBT) segments, functionalized with carboxylic acid anchoring groups, were prepared and anchored to mesoporous TiO2 films to study wavelength-dependent interfacial electron transfer mechanisms. Thin films of the surface-anchored diblock oligomers contained two absorption bands centered at 400 and 500 nm, corresponding to the Tn and TBT blocks, respectively. Pulsed-laser excitation of the oligomer-sensitized films yielded local excited-states that promoted electron injection into TiO2. The injection pathway was dependent on the excitation wavelength, as electron injection occurred from the oligomer block that was locally excited. Recombination between the injected electron and the oxidized oligomer was sensitive to the bridging unit that separates the oligomer conjugated segments (-C≡C- vs trans-Pt(PBu3)2-). When the bridge facilitated strong coupling between the two blocks (-C≡C- bridge), the excitation wavelength had no effect on the recombination pathway, as the hole was delocalized over the entire oligomer. However, in the weak coupling case (Pt(PBu3)2- bridge), selective excitation resulted in wavelength-dependent hole localization that persisted to the μs time scale, providing control over the recombination pathway by varying the excitation wavelength. Dye-sensitized solar cells (DSSCs) were fabricated by using the diblock oligomers as sensitizers. The photocurrent action spectra were measured, and the absorbed photon-to-current efficiency (APCE) provided further insight into the electron-transfer mechanisms that are operative under continuous illumination.

Tightly Connected Poly(3‐Thiophene Boronic Acid)/g‐C3N4 Heterojunctions for Enhanced Visible‐Light Photocatalytic Hydrogen Production

AbstractConstructing efficient polymer semiconductor/g‐C3N4 heterojunctions is highly desirable for enhancing the photogenerated charge separation of g‐C3N4 and further improving the solar‐hydrogen production efficiency. Herein, we synthesized poly(3‐thiophene boronic acid)/g‐C3N4 (PTBA/CN) heterojunctions with tight interface contact by a simple wet‐chemical strategy. The resulting ratio‐optimized 3PTBA/CN heterojunction exhibits 8.7 times enhancement of the visible‐light photocatalytic hydrogen production compared to CN. Based on the steady‐state surface photovoltage spectra (SS‐SPS), photoluminescence spectra (PL), ⋅OH amount measurements, time‐resolved photoluminescence spectra (TR‐PL), and single‐wavelength photocurrent action spectra, it is confirmed that the enhanced photocatalytic performance is mainly attributed to the promoted photogenerated charge separation resulting from the transfer of high‐level electrons from CN to PTBA via the formed tight interface contact, depending on the hydrogen bonding interactions between the boronic acid groups [−B(OH)2] of PTBA and the amino groups (−NH2) of CN. Furthermore, the −B(OH)2 of PTBA facilitates the uniform dispersion of the co‐catalyst Pt. This work provides an effective strategy for constructing efficient tightly connected polymer semiconductor/CN heterojunction photocatalysis.

Improved Visible-Light Photocatalytic H2 Evolution of G-C3N4 Nanosheets by Constructing Heterojunctions with Nano-Sized Poly(3-Thiophenecarboxylic Acid) and Coordinating Fe(III).

It is highly desirable to enhance the photogenerated charge separation of g-C3N4 by constructing efficient heterojunctions, especially with an additional organic constitution for solar-hydrogen conversion. Herein, g-C3N4 nanosheets have been modified controllably with nano-sized poly(3-thiophenecarboxylic acid) (PTA) through in situ photopolymerization and then coordinated with Fe(III) via the -COOH groups of modified PTA, forming an interface of tightly contacted nanoheterojunctions between the Fe(III)-coordinated PTA and g-C3N4. The resulting ratio-optimized nanoheterojunction displays a ~4.6-fold enhancement of the visible-light photocatalytic H2 evolution activity compared to bare g-C3N4. Based on the surface photovoltage spectra, measurements of the amount of •OH produced, photoluminescence (PL) spectra, photoelectrochemical curves, and single-wavelength photocurrent action spectra, it was confirmed that the improved photoactivity of g-C3N4 is attributed to the significantly promoted charge separation by the transfer of high-energy electrons from the lowest unoccupied molecular orbital (LUMO) of g-C3N4 to the modified PTA via the formed tight interface, dependent on the hydrogen bond interaction between the -COOH of PTA and the -NH2 of g-C3N4, and the continuous transfer to the coordinated Fe(III) with -OH favorable for connection with Pt as the cocatalyst. This study demonstrates a feasible strategy for solar-light-driven energy production over the large family of g-C3N4 heterojunction photocatalysts with exceptional visible-light activities.

Controllable synthesis of CuPc/N-rich doped (0 0 1) TiO2 S-scheme nanosheet heterojunctions for efficiently wide-visible light-driven CO2 reduction

Inspired by natural photosynthesis, the rational design of efficient S-scheme heterojunctions holds promises for CO2 conversion by utilizing solar light. Herein, nitrogen-rich doped 001-exposed anatase nanosheets (NPT) have been designed and fabricated by post-treatment with NH3 at a high temperature of 600 °C to phosphate modified TiO2 firstly, and then controllably coupled with copper phthalocyanine (CuPc) via a hydroxyl-induced assembly process to construct a wide-visible-light responsive heterojunction towards CO2 conversion. The optimized CuPc/NPT heterojunction achieves a high production rate of CO (∼5 μmol/g/h) under visible light irradiation, with ∼9-fold enhancement compared with generally N-doped TiO2. Based on the experimental results mainly from photocurrent action spectra, electron paramagnetic resonance measurements, electrochemical reduction curves and in-situ diffuse reflectance infrared Fourier transform spectra, it is confirmed that the exceptional photoactivity is attributed to the N-rich doping for increasing visible-light absorption of TiO2, the effective S-scheme charge transfer from the closely-contacted CuPc/NPT heterojunction with wide visible-light absorption, and subsequently to the electron transfer from the Pc ligand to central metal Cu2+ with good catalytic function for CO2 reduction. This work provides feasible routes for the design and preparation of TiO2-based photocatalysts for solar-driven CO2 conversion.

Improved visible-light activities of ultrathin CoPc/g-C3N4 heterojunctions by N-doped graphene modulation for selective benzyl alcohol oxidation

The interface modulation is the key factor affecting the photoactivity of metal phthalocyanine (MPc)/g-C3N4 heterojunctions for aerobic selective alcohol oxidation. Here, we have successfully fabricated the N-doped graphene-modulated CoPc/g-C3N4 nanosheets (CoPc/NG/CN) heterojunctions. Optimal CoPc/NG/CN photocatalyst demonstrates approximately fourfold photoactivity improvement for benzyl alcohol oxidation with ∼99% selectivity toward benzyl aldehyde and of approximately ninefold 2,4-dichlorophenol degradation rate compared with bare CN, using O2 as oxidant. By means of steady-state surface photovoltage responses in N2 atmosphere, time-resolved photoluminescence spectra, single-wavelength photocurrent action spectra, and electrochemical O2 reduction measurements, it is confirmed that the exceptional photoactivities of resulting CoPc/NG/CN heterojunction are attributed to the facilitated interfacial charge transfer between CoPc and CN by the modulation of NG with favorable electron-induced capacity. In addition, more enriched hydroxyl groups of NG by N doping could induce high dispersion of CoPc molecules via H-bonding effect, resulting in the increase of exposed number of CoPc as visible-light absorption units and single Co2+ sites as catalytic centers for O2 activation so as to further benefit the photocatalytic oxidation processes. This work provides a feasible interfacial modulation strategy to fabricate efficient supported MPc-based heterojunction photocatalyst nanomaterials.

Controlled Construction of Copper Phthalocyanine/α‐Fe2O3 Ultrathin S‐Scheme Heterojunctions for Efficient Photocatalytic CO2 Reduction under Wide Visible‐Light Irradiation

The wide visible‐light‐driven CO2 reduction to acquire solar fuels is a highly desired green route. Herein, novel ultrathin copper phthalocyanine (CuPc)/α‐Fe2O3 heterojunctions as efficient wide visible‐light‐driven photocatalysts for CO2 reduction are controllably synthesized by the hydroxyl‐induced self‐assembly of CuPc onto ultrathin α‐Fe2O3 as‐pre‐prepared through an Al3+‐regulated hydrothermal method. The optimized CuPc/Fe2O3 heterojunction exhibits about 15‐fold high photoactivity for reducing CO2 to CO and CH4 compared with reported Fe2O3 nanoparticles. The exceptional photoactivity is mainly attributed to the enhanced S‐scheme charge transfer and separation in the resulting closely contacted heterojunction, the extended visible‐light range from molecularly disperse CuPc, and its provided central metal cation (Cu2+) with favorable catalytic function for CO2 activation, mainly by means of the dual‐wavelength photocurrent action spectra, the electrochemical reduction tests, and the in situ diffuse reflectance infrared Fourier transform spectra (DRIFTS). This investigation provides new insight about designing and constructing novel metal phthalocyanine (MPc)‐involved S‐scheme heterojunction photocatalysts.

Gold modified TiO2/g-C3N4 for enhanced photocatalytic activities to evolved H2 fuel

Plasmonic Au/TiO2/g-C3N4 nanocomposites have been successfully prepared by simple hydrothermal method. It is demonstrated that the as-synthesized nanocomposites show significant co-catalyst-free photocatalytic activities for H2 evolution under visible-light. The amount-optimized 1Au/4TiO2/g-C3N4 nanocomposite evolved 250-µmol.g-1h−1 H2 at λ > 400 light illumination. The improved photocatalytic activities for H2 evolution is attributed to the greatly-enhanced photoexcited charge separation by electron transfer from Au surface plasmon (~520 nm) and CN (470 nm > λ > 400) to TiO2. Based on the surface photovoltage spectra, photoelectrochemical I-V curves, hydroxyl radical amounts related spectra, and photocurrent action spectra, it is suggested that the fabricated Au/TiO2/g-C3N4 nanocomposite provide a proper energy platform for the photocatalytic H2 production. Moreover, TiO2 is much superior as compare to other wide-band gap metal oxides as energy platforms, like SnO2 and ZrO2. This work would provide a feasible strategy to synthesize an efficient plasmonic-assisted CN-based nanophotocatalyst for solar fuel production.

Improved photocatalytic activities of recyclable porous Fe2O3 nanotubes by modifying with nano-sized SiO2 and g-C3N4 for degrading 2-chlorophenol

It is highly desired to fabricate efficient α-Fe2O3-based photocatalysts with recyclable feature for pollutants degradation. Herein, porous α-Fe2O3 nanotubes with high photocatalytic activity for degrading 2-chlorophenol (2-CP) have been successfully synthesized by a phase separation electrospinning process, with a pipe diameter of about 200 nm . The photoactivity is greatly improved by in-situ introducing SiO2, attributed to the increased surface area by decreasing the size of nanoparticles shell from ~ 30 to 15 nm. Furthermore, the photoactivity of SiO2 modified α-Fe2O3 is further improved by coupling with porous g-C3N4 nanosheets, ascribed to the promoted charge separation by the newly accepted S-scheme charge transfer mainly based on the EPR tests and photocurrent action spectra. Interestingly, the optimized α-Fe2O3-based nanotubes exhibit ~ 4-time improvement of the kinetic rate constant in 2-CP degradation compared with the reported α-Fe2O3 nanoparticles, with good recyclability by self-sediment.

Controlled Synthesis of Nitro-Terminated Poly[2-(3-thienyl)-ethanol]/g-C3N4 Nanosheet Heterojunctions for Efficient Visible-Light Photocatalytic Hydrogen Evolution

Exploration of closely contacted polymeric nanoheterojunctions with suitable frontier molecular orbital energy levels is highly desired for promoting the carrier separation and further improving the photocatalytic performance. In our work, poly[2-(3-thienyl)ethanol]/g-C₃N₄ (PTEtOH/g-C₃N₄) nanosheet heterojunctions were successfully fabricated using a controlled surface hydroxyl-induced assembly process and displayed obviously improved visible-light performance for H₂ evolution. As verified by time-resolved photoluminescence spectra, surface photovoltage spectra and •OH amount measurements, the improved performance is due to the promoted photogenerated carrier transfer and separation in the synthesized PTEtOH/g-C₃N₄ heterojunction with strengthened interface contacts via hydrogen bonding. Furthermore, single-wavelength photocurrent action spectra were performed to confirm that the promoted photogenerated carrier separation is mainly dependent on the excited high-level electron transfer from g-C₃N₄ to PTEtOH. Interestingly, the photocatalytic performance is further improved by synthesizing nitro-terminated PTEtOH (N-PTEtOH) with lowered LUMO energy level and decreased particle size and then constructing N-PTEtOH/g-C₃N₄ nanosheet heterojunction, exhibiting a factor-of-15 enhancement, in comparison with that of g-C₃N₄ and obvious superiority to reported photoactivities. Noteworthily, abundant hydroxyl groups on the surface of the heterojunctions are beneficial for the uniform deposition of Pt nanoparticles as co-catalysts and hence for photocatalytic reactions. This study offers a feasible strategy to design efficient polymeric heterojunctions as nanophotocatalysts for solar-light-driven energy production.

An insight in photocurrent generation mechanism on Cu2O quantum dot sensitized Cu/p-CuI photo-electrochemical cell and efficient H2 generation at Cu/p-CuI/Cu2O electrolyte interface

p-CuI (band gap ≈ 3.1 eV) is sensitised with quantum dots (QDs) of Cu2O (band gap ≈ 2.0 eV) as a novel hybrid strategy to make photoelectrochemical cells. In which, p-CuI thin film was deposited by immersing a cleaned copper sheet into a solution containing I2 (10−2 M), KI (0.1 M), CuSO4 (10−3 M) to make Cu/p-CuI photoelectrodes. To fabricate Cu/p-CuI/Cu2O photoelectrodes, Cu/p-CuI photoelectrodes were boiled in a CuSO4 (10−2 M) solution at different time intervals. When gradually increases the boiling time until 5 min, the size of the p-CuI microcrystals decreases with the formation of Cu2O QDs on p-CuI microcrystals. When the boiling period exceeds 5 mins, Cu2O QDs convert gradually into micro-crystals and covering p-CuI thin film. Variations in the photocurrent quantum efficiency (Φ%) with the Cu2O amount fabricated on p-CuI thin layer were monitored. The photophysical and photochemical processes associated at Cu/p-CuI/Cu2O-electrolyte interface are presented to delineate the sensitisation of p-CuI wide band gap semiconductor with Cu2O QDs produced. Our recent explanation on the kinetics of the photocurrent generation by dye sensitised solar cells using CAN’s model equation Φ = AD0 – BD02, was used to describe the QD sensitisation of p-CuI by Cu2O QDs. It was experimentally confirmed that CAN’s constant ‘A’ relates with the photocurrent generation processes and the CAN’s constant ‘B’ associated with the processes in suppression of photocurrent generation. Material characterisation from Scanning Electron Microscopy (SEM), Field Emission Scanning Electron Microscopy (FESEM), X-ray Diffraction (XRD), UV absorption, photocurrent action spectra, and photoelectrochemical (PEC) measurements through I-V characteristics are presented to confirm the formation of Cu/CuI/Cu2O electrodes. A remarkable H2 generation was noticed in the presence of 0.025 M Na2SO4 solution, from the QDs sensitised photogenerated electrons at Cu/p-CuI/Cu2O-electrolyte interface. The mechanism of H2 generation is confirmed with the energy band positions of p-CuI and Cu2O QDs under visible light irradiation. Different H2 profiles are presented in detail with the size of QDs fabricated on p-CuI.

Optimization of semiconductor–electrolyte interfacial phenomena for stable and efficient photoelectrochemical water oxidation behavior of Bi2Mo2O9–Bi2MoO6 heterojunction

Bismuth molybdates are considered the essential photocatalysts due to their mesoporous structure, low energy gap, suitable ion conductions, acousto-optics, photo-conduction, and sensing properties. The present report describes a cost-effective route for developing stable and efficient photocatalysts for optical to chemical energy conversion and environmental purification. In this work, we have developed nano-structured mixed bismuth molybdates with different thicknesses in the presence of TX-100 as the surfactant through drop-cast route taking bismuth nitrate and ammonium molybdate as the precursors. Final products were subsequently dried and annealed in air at 600 °C for 3 h. The semiconductors’ photoelectrochemical performance was measured under periodic illumination in the presence of Na2SO4 (0.1 M) solution and (0.1 M) Na2SO3 with 0.1 M Na2SO4 for water and sacrificial oxidation, respectively. These materials exhibit noticeable photocatalytic activity even after successive runs, indicating stable behavior. The materials are composed of Bi2Mo2O9–Bi2MoO6 heterostructures and the film with optimized thickness yields a photocurrent of 220 µA/cm2 at 1.3 V. This value is exceptionally higher in magnitude than the literature reports employing conventionally prepared bismuth molybdates (1.8 µA/cm2). Electrochemical impedance and photocurrent action spectra support a noticeable photon to current conversion efficiencies of the materials under illumination.

Syntheses and Photoelectrochemical Properties of Plasmonic Molybdenum Oxide Nanoparticles Via Ionic Liquid/Metal Sputtering

Introduction Incident lights interact with noble metal nanoparticles (NPs) to form collective oscillations of free electrons, creating a strong electromagnetic field on their surface. This phenomenon is called localized surface plasmon resonance (LSPR). Recently metal oxide NPs with appreciable concentration of free electrons have been also reported to exhibit LSPR peaks, the peak wavelengths of which were controlled from the visible to near-IR regions.[1] When a plasmonic NP was combined with a semiconductor, the excitation of LSPR could cause the injections of electrons and/or holes from plasmonic NPs to the semiconductor, that is, the plasmon-induced charge separation (PICS).[2] Since the PICS was reported using plasmonic metal oxide NPs,[3] the intense research has been devoted to studying plasmonic metal and metal oxide NPs for the application to photovoltaics, photocatalyts, and biosensors.Recently we reported the preparation of noble metal NPs by metal sputtering deposition onto room-temperature ionic liquids (RTIL) under a reduced pressure (RTIL/metal sputtering), where NPs of several nanometers in size were stably and uniformly dispersed without additional stabilizing agents.[4] This technique enabled the clean preparation of plasmonic metal NPs, such as Au[4], Ag[5], and AgAu alloy[6]. In this study, we apply the RTIL/metal sputtering to the preparation of molybdenum oxide (MoOx) NPs. Thus-obtained NPs exhibited the LSPR peak, the excitation of which induced the PICS. Experimental The sputter deposition of molybdenum were carried out on the surface of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate (HyEMI-BF4) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4) used as RTILs for 1 h with a discharge current of 30 mA under an argon pressure of 3.0 Pa. The deposited NPs were partially oxidized by the heat treatment at 473 K for 30 min in air, resulting in the formation of MoOx NPs. The photoelectrochemical properties were measured in a 0.5 M Na2SO4 aqueous solution with the ITO electrode immobilized with MoOx NPs as working electrodes, a Pt counter electrode and a Ag/AgCl reference electrode. The photocurrents were detected with monochromatic light irradiation under the potential application at +0.5 V vs Ag/AgCl. Results and Discussion TEM measurements revealed that Mo NPs sputter-deposited in HyEMI-BF4 had an average diameter of 6.8 nm and then the heat treatment at 473 K increased the particle size to ca. 65 nm. XPS spectra of thus-obtained particles indicated that the thus-obtained NPs were composed of MoOx containing Mo(V) and Mo(VI) species. The MoOx NPs prepared in HyEMI-BF4 showed a LSPR peak at around 840 nm, the peak wavelength of which was close to that of LSPR reported for chemically synthesized MoO3-x NPs.[1] On the other hand, MoOx NPs prepared in EMI-BF4 showed no LSPR peak in the visible and near-IR regions. Anodic photocurrents were observed by the irradiation to MoOx NP-immobilized ITO electrodes with wavelength shorter than ca. 1000 nm. Regardless of the kinds of MoOx NPs, the action spectra of photocurrents showed the increase of IPCE at the wavelength below 600 nm due to the photoexcitation of interband transition of MoO3, being in agreement with their extinction spectra. Furthermore, the MoOx NPs prepared in HyEMI-BF4 showed a peak at 840 nm, the peak wavelength of which agreed with that of their LSPR peak. In contrast, MoOx NPs formed in EMI-BF4 exhibited no photocurrent by the irradiation of near-IR lights.Conclusively, we successfully prepared the MoOx NPs with RTIL/metal sputtering technique followed by the heating treatment. The NPs formed in HyEMI-BF4 showed the LSPR peak in near-IR region, the photoexcitation of which induced the PICS from the MoOx NPs to the ITO electrodes. References (1) A. Agrawal, S. H. Cho, O. Zandi, S. Ghosh, R. W. Johns, and D. J. Milliron, Chem. Rev., 118, 3121 (2018).(2) Y. Tian and T. Tatsuma, J. Am. Chem. Soc., 127, 7632 (2005).(3) S. H. Lee, H. Nishi, and T. Tatsuma, Nanoscale, 10, 2841 (2018).(4) T. Torimoto, K. Okazaki, T. Kiyama, K. Hirahara, N. Tanaka, and S. Kuwabata, Appl. Phys. Lett., 89, 243117 (2006).(5) T. Suzuki, K. Okazaki, T. Kiyama, S. Kuwabata, and T. Torimoto, Electrochemistry, 77, 636 (2009).(6) K. Okazaki, T. Kiyama, K. Hirahara, N. Tanaka, S. Kuwabata, and T. Torimoto, Chem. Commun., 6, 691 (2008).

Porous two-dimension MnO2-C3N4/titanium phosphate nanocomposites as efficient photocatalsyts for CO oxidation and mechanisms

Herein, two-dimension (2D) δ-MnO2-modified porous g-C3N4/micro-mesoporous titanium phosphate (MO-CN/TiP) nanocomposites have been controllably fabricated by a two-step solvothermal process. The amount-optimized MO-CN/TiP nanocomposite exhibits greatly improved photocatalytic CO oxidation performance (87%) compared with corresponding bare TiP and CN/TiP, even superior to the commercial P25 TiO2. Based on the experimental results of time-resolved surface photovoltage responses, photocurrent action spectra, and electron paramagnetic resonance signals, it is clearly confirmed that the exceptional photoactivity is mainly attributed to the great promotion in the Z-scheme charge transfer in resultant dimension-matched CN/TiP nanocomposite and in the O2 activation via the modified MO. The porous structure favorable to increase the specific surface areas and to facilitate the mass diffusion and the extended visible-light absorption also contribute to the photoactivity enhancement. Moreover, it is uncovered by the in-situ diffuse reflectance fourier transform infrared spectra that CO is previously adsorbed by the formed OHOC intermediate with the surface hydroxyls and then oxidized.

Mg-O-Bridged Polypyrrole/g-C3 N4 Nanocomposites as Efficient Visible-Light Catalysts for Hydrogen Evolution.

It is highly desired to improve the visible-light activity of g-C3 N4 for H2 evolution by constructing closely contacted heterojunctions with conductive polymers. Herein, a polymer nanocomposite photocatalyst with high visible-light activity is fabricated successfully by coupling nanosized polypyrrole (NPPy) particles onto g-C3 N4 nanosheets through a simple wet-chemical process, and its visible-light activity is improved further by constructing Mg-O bridges between the NPPy and g-C3 N4 . The amount-optimized bridged nanocomposite displays an approximately ninefold improvement in visible-light activity compared with g-C3 N4 . On the basis of transient-state surface photovoltage responses, photoluminescence spectra, . OH amount evaluation, and photoelectrochemical curves, it is concluded that the exceptional photoactivity can be attributed to the significantly promoted charge transfer and separation along with visible photosensitization from NPPy. Interestingly, it is confirmed that the promoted charge separation depends mainly on the excited high-level electron transfer from g-C3 N4 to NPPy by single-wavelength photocurrent action spectra. This work provides a feasible strategy for designing polymer nano-heterojunction photocatalysts with exceptional visible-light activities.

Ultrafine SnO2/010 Facet-Exposed BiVO4 Nanocomposites as Efficient Photoanodes for Controllable Conversion of 2,4-Dichlorophenol via a Preferential Dechlorination Path.

It is a great challenge for achieving efficiently controllable conversion of chlorinated organics through BiVO4-based photoelectrochemical methods by improving the selective adsorption of such organics and charge separation. Herein, we have successfully fabricated SnO2/010 facet-exposed BiVO4 nanocomposites by a series of hydrothermal processes and further used as efficient photoanodes. The resulting photoanode exhibits about 6.3 times higher photoelectrochemical activity than bulk-BiVO4, especially with the efficiently controllable conversion of 2,4-dichlorophenol (2,4-DCP) to the nontoxic valuable intermediates such as catechol and pyrogallol by preferential dechlorination. Based on the 2,4-DCP adsorption curves, in situ diffuse reflectance infrared spectra, transient-state surface photovoltage responses, and photocurrent action spectra, it was clearly confirmed that the exceptional performance could be mainly attributed to the promoted selective adsorption of 2,4-DCP for efficiently modulating holes by the strong coordination interactions between -Cl with lone-pair electrons in 2,4-DCP and Bi- with empty orbits on (010) facet-exposed BiVO4 nanoflakes and to the coupled nano-SnO2 for prolonging the charge lifetime of BiVO4 by acting as the high-energy-level electron-accepting platform. This work provides a feasible strategy to develop excellent BiVO4-based photoelectrochemical methods for efficiently controlling the conversion of chlorinated organics simultaneously with energy production and recovery.

Synthesis of nanosized Ag-modified 2D/2D hydroxylated g-C3N4/TS-1 Z-scheme nanocomposites for efficient photocatalytic CO2 reduction

It is significant to enhance the charge separation and extend the visible-light range for the TS-1 molecular sieve-based photocatalysts to improve the photocatalytic performance for CO2 reduction reaction (CO2RR). Here, dimension-matched 2D/2D hydroxylated g-C3N4/TS-1 (hCN/TS-1) nanocomposites have been successfully fabricated and further modified by nanosized Ag by the photoreduction method. The optimum Ag-modified hCN/TS-1 exhibits ∼ 7-time CO2 conversion than that of 2D TS-1. Based on the surface photovoltage responses, monochromatic photocurrent action spectra and electrochemical reduction curves, it is confirmed that the exceptional photoactivity is attributed to the greatly-enhanced charge separation via the Z-scheme mode between hCN and TS-1 at intimately-connected interfaces, extended visible-light absorption endowed by hCN, and Ag nanoparticles as the effective electron capturers with favorable catalytic function for activating CO2 molecules. This work showcases an effective and feasible design strategy to fabricate highly effective TS-1 molecular sieve-based photocatalysts for practical application.

Engineering Cells, Membranes and Light Harvesting/Photosystem II Super-Complexes in Bio-Photoelectrochemical Cells

Photosynthetic organisms, membranes and complexes are attractive starting materials for solar energy conversion (SEC). Our overall goal is to develop methods to perform SEC using these materials in simple, inexpensive and a fashion that will be non-polluting and will not compete with the growth of food materials. I will describe here how the remarkable photocatalytic activity of the photosynthetic apparatus can provide overall water splitting with oxygen and hydrogen production in Bio-Photo-Electro-Chemical (BPEC) cells via the simplest and cleanest of processes wither in the absence or presence of added electron transport molecules. With plant thylakoids, electrons are shuttled by FeCN to a transparent FTO electrode, yielding a photocurrent density of 0.5 mA·cm-2. Hydrogen evolution occurs at the cathode at a bias as low as 0.8 V. A tandem cell comprising the BPEC cell with the thylakoid membranes and a Si photovoltaic module achieves overall water splitting with solar to hydrogen conversion efficiency of 0.3% (Pinhassi et al. Nature Communications 2016). With cyanobacterial cells, following a brief treatment that does not induce loss of cell viability, electrons from both the respiratory and photosynthetic systems are transferred directly to a graphite electrode, utilizing endogenous electron carriers (Saper et al. Nature Communications 2018). The current produced can be used for hydrogen production at low additional bias for significantly longer durations than the plant thylakoids.Another route is to isolate the photosynthetic complexes and chemically connect them to the electrochemical cell. One of the issues with this strategy is the small number of light absorbing chromophores connected to the complex, lowering the photochemical efficiency. Connection of isolated light harvesting complexes can help to overcome this deficiency. Photosystem II (PSII) is the only enzyme that catalyzes light-induced water oxidation being the basis for its application as a biophotoanode in various bio-photovoltaics and photo-bioelectrochemical cells. However, the absorption spectrum of PSII limits the quantum efficiency in the range of visible light, due to a gap in the green absorption region of chlorophylls (500 - 650 nm). To overcome this limitation, we have stabilized the interaction between PSII and Phycobilisomes (PBSs) – the cyanobacterial light harvesting complex, in vitro. The PBS of different cyanobacteria were analyzed for their ability to transfer energy to Thermosynechococcus elongatus (Te) PSII by fluorescence spill-over and photocurrent action spectra. Integration of the PBS-PSII super-complexes within an Os-complex-modified hydrogel on macro-porous indium tin oxide electrodes (MP-ITO) resulted in notably improved, wavelength dependent, incident photon-to-electron conversion efficiencies (IPCE). IPCE values in the green gap were doubled from 3 % to 6 % compared to PSII electrodes without PBS and a maximum IPCE up to 10.9 % at 670 nm was achieved. Figure 1

Controlled synthesis of novel Z-scheme iron phthalocyanine/porous WO3 nanocomposites as efficient photocatalysts for CO2 reduction

Herein, novel Z-scheme iron phthalocyanine (FePc)/porous WO3 nanocomposites as efficient photocatalysts have been controllably synthesized based on the resulting porous WO3 pre-prepared by a hydrothermal process. The key is to make FePc assemble uniformly onto porous WO3 by hydroxyl induction for their close contacts via H-bonding. The optimized 0.8FePc/P-WO3 nanocomposite exhibits about 8-fold high photoactivity for reducing CO2 to CO and CH4 compared with the reported WO3 nanoplate, attributed to the increased specific surface, enhanced charge separation and extended visible-light utilization. Interestingly, the enhanced charge separation mainly depends on the novel Z-scheme transfer process with the un-overlapped optical absorption, along with the provided catalytic function of central Fe2+ in FePc for CO2 reduction mainly by means of the dual wavelength photocurrent action spectra, the electrochemical reduction tests, and the in-situ diffuse reflectance FTIR spectra. Moreover, it is also feasible to replace FePc with other MPcs.

Efficiently photocatalytic degradation of monochlorophenol on in-situ fabricated BiPO4/β-Bi2O3 heterojunction microspheres and O2-free hole-induced selective dechloridation conversion with H2 evolution

Herein, hierarchical BiPO4/β-Bi2O3 microspheres have been successfully synthesized via one-step annealing pyrophosphate anchored (BiO)2CO3 microspheres, and utilized as efficient and recyclable photocatalysts for CPs degradation. Notably, the amount-optimized heterojunctional microspheres display high photocatalytic activity for 2-CP degradation, even with 5-time enhancement compared to the classical TiO2 (P25). By means of the surface photovoltage spectra, photocurrent action spectra and CPs adsorption curves, the exceptional photoactivities are mainly attributed to the strong adsorption of 2-CP due to the complexation of Bi on Bi2O3 with empty orbitals and Cl of 2-CP with lone-pair electrons for efficiently modulating holes, and to the prolonged charge lifetime by transferring the photogenerated proper-energy-level electrons of β-Bi2O3 to the in-situ formed nano-BiPO4. It is confirmed that the photogenerated holes are dominant to induce the degradation of 2-CP on BiPO4/β-Bi2O3, and to initiate the selective conversion to the value-added intermediates like 4-acetoxyphenol on O2-free condition, along with H2 evolution.