Weak Visible Light Research Articles

Boosting photocatalytic hydrogen evolution over 2D/0D graphene/H–In2O3 nanohybrids with regulated oxygen vacancies

Hydrogen is considered as one of the most efficient solutions to the carbon pollution. Indium oxide (In2O3) with good electrical conductivity and stability has great potential in utilization as hydrogen evolution photocatalyst. However, weak visible light response of In2O3-based catalysts limits their applications. Although the hydrogenation is a well-known effective method to enhance the photoresponse of metal oxides, severe instability caused by the unstable oxygen vacancies cannot be ignored. Here, we report the synthesis of graphene/hydrogenated In2O3 (H–In2O3) 2D/0D heterostructure. Interestingly, the introduction of graphene not only facilitates the light absorption and charge separation by the formation of heterojunction, but also regulates the concentration of surface oxygen vacancies. X-ray photoelectron spectra (XPS), electron paramagnetic resonance (EPR), and photoluminescence spectra (PL) are employed to investigate the mechanism. As expected, the prepared graphene/H–In2O3 (GHI) heterojunction shows significantly improved photocatalytic hydrogen evolution activities, and the optimal photocatalytic hydrogen evolution rate is 16.3 times and 2.6 times that of the In2O3 and H–In2O3 sample, respectively. Moreover, the regulation of the surface oxygen vacancies enables the graphene/H–In2O3 to be stable during continuous cycling measurements. These findings shed a light on the design of highly efficient and stable metal oxides based photocatalysts.

From Perylene Diimide Polymers to Fused‐Ring Electron Acceptors: A 15‐Year Exploration Journey of Nonfullerene Acceptors

Comprehensive SummaryFullerene derivatives are classic electron acceptor materials for organic solar cells (OSCs) but possess some intrinsic drawbacks such as weak visible light absorption, limited optoelectronic property tunability, difficult purification and photochemical/morphological instability. Fullerene acceptors are a bottleneck restricting further development of this field. Our group pioneered the exploration of novel nonfullerene acceptors in China in 2006, and initiated the research of two representative acceptor systems, rylene diimide polymer and fused‐ring electron acceptor (FREA). FREA breaks the theoretical efficiency limit of fullerene‐based OSCs (~13%) and promotes the whole field to an unprecedented prosperity with efficiency of 20%, heralding a nonfullerene era for OSCs. In this review, we revisit 15‐year nonfullerene exploration journey, summarize the design principles, molecular engineering strategies, physical mechanisms and device applications of these two nonfullerene acceptor systems, and propose some possible research topics in the near future. What is the most favorite and original chemistry developed in your research group?Fused‐ring electron acceptor for photovoltaics.How do you get into this specific field? Could you please share some experiences with our readers?In 2006 when I came back to ICCAS from USA and started my independent academic career, I was interested in organic photovoltaics (OPV) which I had never touched before since I believed it is useful and should have a bright future. OPV converts renewable solar energy to clean electricity through photovoltaic effect. The active layer in OPV device consists of electron donor and electron acceptor. Although fullerenes were prevailing acceptor materials in OPV at that time, I doubted if this choice is correct considering their fatal flaws such as weak absorption. I was curious about why no research groups in China explored fullerene alternatives before 2006. In 2006 our group initiated the nonfullerene OPVresearch of China. In 2015 we invented the milestone molecule ITIC and pioneered fused‐ring electron acceptor (FREA). Around 300 research groups in >20 countries have utilized the FREA to fabricate high‐efficiency OPV devices with champion efficiency of >20%. The FREA has subverted previously predominant fullerenes, and is inaugurating a new era of the OPV field.How do you supervise your students?I expect that my students should have some essential personalities such as curiosity, creativity, devotion, persistence and diligence. I encourage them to do original, unique and leading research. I endow them with cheerful academic atmosphere such as self‐motivation, open‐mindedness and cross‐cooperation. I would like to provide them with warm human solicitude when they need help or suffer from bitterness.What is the most important personality for scientific research?Curiosity; uniqueness; persistence.

Constructing benzene ring modified graphitic carbon nitride with narrowed bandgap and enhanced molecular oxygen activation for efficient photocatalytic degradation of oxytetracycline

Popular graphitic carbon nitride (g-C3N4) photocatalyst always faces the problems of weak visible light absorption and fast recombination of photogenerated electron-hole pairs. Herein, a novel benzene ring modified g-C3N4 nanosheet (BCNNS) was synthesized by a simple calcination method. The degradation rate of oxytetracycline by BCNNS under visible light can reach 72% (within 60 min), significantly higher than that of the unmodified g-C3N4 nanosheet (50%). And the degradation rate constant of BCNNS is 0.025 min−1, which is 2.1 times higher than that of g-C3N4 (0.012 min−1). The improvement in the photocatalytic degradation performance can be attributed to the introduction of benzene ring, which can significantly broaden the light absorption range and intensify. In addition, the introduction of benzene ring can adjust the original electronic structure, thereby effectively suppressing the recombination of electron-hole pairs. Furthermore, density functional theory (DFT) calculations demonstrate that the introduction of benzene ring can significantly promote the surface adsorption of molecular oxygen and promote the transfer of electrons to molecular oxygen. This demonstrates that the embedded benzene ring can effectually advance the activation of molecular oxygen, which also well confirms that O2− and 1O2 are the main active species in the system of BCNNS photocatalytic degradation of oxytetracycline. This study reveals that benzene ring modified g-C3N4 has great potential in environmental purification, and provides a promising strategy for the removal of stubborn water contaminants.

Linker functionalized poly(heptazine imide) as charge channel and activation site for enhancing photocatalytic nitrogen fixation in pure water

Poly(heptazine imide) as a metal-free semiconductor has stimulated considerable focus in the photocatalytic nitrogen fixation. However, the weak visible light absorption and unordered migration of photogenerated carriers as well as limited active site often resulted in poor photocatalytic performance. Here, we propose a conceptual to construct directional electron delivery channel via introducing C-N and N-C-O units linked terminal melem units (PCON) using a facile copolymerizing method. The optimized PCON achieved excellent photocatalytic nitrogen fixation rate (49.11 μmol g−1 h−1) and near-IR yield in pure water without using cocatalyst, which is 11 times higher than that of pristine C3N4. Based on DFT calculation and experiment results, the superior photocatalytic performance is traced back to the integrated different linker into the framework induced n − π * transitions and acted as charge channel and activation site, which could significantly extend light absorption to the near IR, and enhance charge separation as well as reactive activation. This study lay out the importance of linker engineer of the catalyst to regulate photocatalytic activity over organic-based photocatalysts.

Effect of surface-deposited Ti3C2Tx MXene on the photoelectrochemical water-oxidation performance of iron-doped titania nanorod array

As a promising photoanode material, TiO2 confronts two challenges, weak visible light absorption and low catalytic activity for water oxidation, which limit its photoelectrochemical performance toward water oxidation. Doping and co-catalyst deposition provide effective ways to extending the light-absorption spectral range and accelerating the water-oxidation kinetics, respectively. Herein, an efficient TiO2-based photoelectrode for water oxidation is prepared by Fe doping and electrophoretic Ti3C2Tx deposition. The Fe doping effectively extends the light absorption of TiO2 toward visible region. Owing to the excellent water oxidation activity of Ti3C2Tx, its deposition greatly accelerates the water-oxidation kinetics, which in turn enhances the photocarrier separation and injection efficiencies. The well-designed Fe-TiO2/Ti3C2Tx exhibits a photoelectrochemical current density of 1.23 mA cm−2 at 1.23 V vs. RHE, which is much higher than those of Fe-TiO2. The maximum IPCE value is enhanced from 64.7% of Fe-TiO2 to 92.8% of Fe-TiO2/Ti3C2Tx at 380 nm. Our findings provide an effective way to fabricate efficient photoanode for water oxidation and are helpful to understanding the photoelectrochemical performance of hybrid nanostructures.

Hydrogenated Amorphous Titania with Engineered Surface Oxygen Vacancy for Efficient Formaldehyde and Dye Removals under Visible-Light Irradiation.

Hydrogenated crystalized TiO2−x with oxygen vacant (OV) doping has attracted considerable attraction, owing to its impressive photoactivity. However, amorphous TiO2, as a common allotrope of titania, is ignored as a hydrogenated templet. In this work, hydrogenated amorphous TiO2−x (HAm-TiO2−x) with engineered surface OV and high surface area (176.7 cm2 g−1) was first prepared using a unique liquid plasma hydrogenation strategy. In HAm-TiO2−x, we found that OV was energetically retained in the subsurface region; in particular, the subsurface OV-induced energy level preferred to remain under the conduction band (0.5 eV) to form a conduction band tail and deep trap states, resulting in a narrow bandgap (2.36 eV). With the benefits of abundant light absorption and efficient photocarrier transportation, HAm-TiO2−x coated glass has demonstrated superior visible-light-driven self-cleaning performances. To investigate its formaldehyde photodegradation under harsh indoor conditions, HAm-TiO2−x was used to decompose low-concentration formaldehyde (~0.6 ppm) with weak-visible light (λ = 600 nm, power density = 0.136 mW/cm2). Thus, HAm-TiO2−x achieved high quantum efficiency of 3 × 10−6 molecules/photon and photoactivity of 92.6%. The adsorption capabilities of O2 (−1.42 eV) and HCHO (−1.58 eV) in HAm-TiO2−x are both largely promoted in the presence of subsurface OV. The surface reaction pathway and formaldehyde decomposition mechanism over HAm-TiO2−x were finally clarified. This work opened a promising way to fabricate hydrogenated amorphous photocatalysts, which could contribute to visible-light-driven photocatalytic environmental applications.

Ultrasensitive photochromism and impedance dual response to weak visible light by solvated Pb(II) modified polyoxomolybdate

Polyoxometalates (POMs) are important inorganic photochromic materials to be potentially applied in photo-induced switch, energy storage, and even the detection of light. However, due to the limited sensitivity of POMs, it is difficult to realize the photochromic response to weak visible light. In this paper, by the coordination of solvated Pb(II), a new structure-defined chain-like polyoxomolybdate complex of [(Pb(DMF)4)3(P2Mo18O62)2]n (Pb3Mo18, DMF = dimethylformamide) has been demonstrated by a facile solvent-diffusion approach. By virtue of interactions between Pb(DMF)4 and polyoxoanions, Pb3Mo18 shows an ultrasensitive photochromic response to weak visible lights and forms the reduced 'heteropoly blue' species through ligand-to-metal charge transfer (LMCT) process. A new mechanism is firstly proposed here that the 6s orbital lone electron pair on Pb(II) can effectively stabilize the generated hole of oxygen atoms as a result of O→Mo charge transfer. Through the proposed mechanism, the LMCT barrier is drastically lowered and allows the coloration to be occurred even upon weak visible light. Also, because the conductivity of Pb3Mo18 enhances with the increase of reduction extent, its electrochemical impedance signals are proportionally response to irradiation intensity. Especially, for the first time, the polyoxomolybdate composite can be used to detect weak visible light, in which the optical signal can be converted into electrical signal output. Moreover, Pb3Mo18 can be drip-coated on the surface of the screen printed chip electrode, which is facile to the detection of light by portable devices compatible with computers, mobile phones and other electronic equipment. This work not only highlights a new approach to the molecular design of photochromic POMs by the coordination of metal ions with the effect of inert electron pair, but also lays a foundation to extend the application of POMs as light signal sensors.

Weak-light-driven Ag–TiO2 photocatalyst and bactericide prepared by coprecipitation with effective Ag doping and deposition

TiO2 can mainly absorb ultraviolet light (UV) and thus the strong light irradiation of photocatalyst is highly needed to obtain efficient charge carrier (electrons and holes) production for subsequent reactions. In this paper, Ag–TiO2 nanoparticles with high Ag dispersibility were prepared by different Ag contents (0–6 at. %) and calcination temperatures (200–600 °C) using a coprecipitation method. Results showed that Ag inhibited the transformation of anatase to rutile TiO2, resulting in the decreased Eg and increased amounts of chemisorbed hydroxyl oxygen as well as oxygen vacancy. 2% Ag–TiO2 possessed the best and high photocatalytic efficiency under weak UV and visible light irradiation (15W). The bactericidal activity of Ag–TiO2 nanoparticles was also enhanced compared with pure TiO2, and further enhanced with Ag content. The superior performance was mainly ascribed to the synergistic effect of Ag and TiO2.

Photo-modulation of supramolecular polymorphism in the self-assembly of a scissor-shaped azobenzene dyad into nanotoroids and fibers.

Recent advances in the research field of supramolecularly engineered dye aggregates have enabled the design of simple one-dimensional stacks such as fibers and of closed structures such as nanotoroids (nanorings). More complex and advanced supramolecular systems could potentially be designed using a molecule that is able to provide either of these distinct nanostructures under different conditions. In this study, we introduced bulky but strongly aggregating cholesterol units to a scissor-shaped azobenzene dyad framework, which affords either nanotoroids, nanotubes, or 1D fibers, depending on the substituents. This new dyad with two trans-azobenzene arms shows supramolecular polymorphism in its temperature-controlled self-assembly, leading to not only oligomeric nanotoroids as kinetic products, but also to one-dimensional fibers as thermodynamic products. This supramolecular polymorphism can also be achieved via photo-triggered self-assembly, i.e., irradiation of a monomeric solution of the dyad with two cis-azobenzene arms using strong visible light leads to the preferential formation of nanotoroids, whereas irradiation with weak visible light leads to the predominant formation of 1D fibers. This is the first example of a successful light-induced modulation of supramolecular polymorphism to produce distinctly nanostructured aggregates under isothermal conditions.

Triplet Photosensitizers Showing Strong Absorption of Visible Light and Long-Lived Triplet Excited States and Application in Photocatalysis: A Mini Review

Triplet photosensitizers (PSs) have been studied as photocatalysts in photocatalytic H2 evolution by water splitting and photoredox catalytic synthetic organic reactions, etc. The applications share common features that the photocatalysts (triplet PSs) harvest the photoexcitation energy, then undergo intersystem crossing (ISC), and finally initiate the electron transfer or triplet energy transfer, which are intermolecular processes in most cases. Thus, triplet PSs showing a strong visible-light-harvesting ability and long triplet excited state lifetimes are desired because they can enhance the above intermolecular processes. The conventional transition metal complexes (i.e., Ru(bpy)3X2 or Ir(ppy)3) have been widely used; however, these complexes are not satisfactory due to their weak absorption of visible light and short triplet excited state lifetimes. To a large extent, the photophysical property of these complexes is due to the low-lying metal-to-ligand charge transfer (MLCT) state, the S0 → 1MLCT transition is weakly allowed, and a strong heavy atom effect exists for the 3MLCT state, which results in weak visible light absorption and a short triplet excited state lifetime, respectively. This mini review introduces the recent progress of the development of the transition metal complexes as well as the organic triplet PSs that show a strong visible-light-harvesting ability and long triplet excited state lifetimes. The application of these new triplet PSs in photocatalytic H2 evolution and photoredox catalytic synthetic organic reactions is summarized.

Engineering 2D compressed layered g-C3N4 nanosheets by the intercalation of BiVO4-Bi2WO6 composites for boosting photocatalytic activities

The traditional bulk graphitic carbon nitride has disadvantages of weak visible light absorption ability and fast charge carrier recombination speed, which greatly limit its further industrial application. In this work, we successfully construct a new ternary heterojunction photocatalyst that 2D compressed layered g-C3N4 nanosheets (CNNs) are modified by the intercalation of BiVO4-Bi2WO6 composites (CVW-I) through one-step hydrothermal method, in which the bismuth precursors are introduced and confined in the interlayer of CNNs and hence the compressed adjacent layers are formed simultaneously in CNNs. Since the close contact of different components with compressed carbon nitride layers, the built-in electric field is relatively formed and the recombination rate between photogenerated electrons and holes is remarkably suppressed. Attributing to these improvements, the as-constructed CVW-I composite achieves more striking photocatalytic activity, and the rate constant of CVW-I reached the highest values for RhB and TC degradation (k = 0.058 min−1 and 0.048 min−1), which are 4.5 and 3.6 times higher than those of carbon nitride, respectively.

Facile hydrothermal preparation of a ZnFe2O4/TiO2 heterojunction for NOx removal

Titanium dioxide (TiO2) has become the most promising photocatalyst. It is non-toxic and has a wide range of sources, but its application is limited due to its weak visible light absorption capacity. Compounding with other materials to form heterojunctions has proven to be effective strategies for enabling high photocatalytic performances under visible light. Here, the ZnFe2O4/TiO2 composites had been synthesized by a facile hydrothermal method to realize efficient visible light photocatalytic activity of NOx removal. A series of characterizations, such as XRD, ESR, in-situ DRIFTS, etc., were used to analyze the physical and chemical properties of the photocatalyst, which demonstrated that the composite material had more active sites and a faster electron transfer rate. The optimal sample (12 wt% ZnFe2O4/TiO2) had a NOx removal rate of 54 % nearly 11 times higher than that of original TiO2. On the basis of the above photocatalytic experimental results and characterizations, a possible mechanism or pathway was proposed and illustrated. This work can provide a feasible strategy to prepare TiO2-based composite materials with magnetic separation properties to effectively remove NOx.

Low-cost and large mass producible phenolic resin for water disinfection and antibacterial coating under weak visible light LED or sunlight irradiation

In present study, we for the first time discovered the photocatalytic water disinfection and antibacterial ability of phenolic-formaldehyde (PR) resins irradiated by LED lamp or natural sunlight in various application modes. The novel narrow band-gap, low-cost and large mass easily producible resin photocatalysts exhibit advanced and stable Escherichia coli (E. coli) inactivation performance, which is better than some well-known metal and non-metal based visible light photocatalysts under the identical condition. We have provided a proof-of-concept demonstration of its practical application feasibility for water purification in both immobilized plastic bag and continuous flow-through reactor under weak LED lamp or natural sunlight irradiation. Furthermore, the PR resin coating film exhibits remarkable E. coli deactivation property under weak LED lamp irradiation. This work provides a new approach for developing resin-based products with antibacterial function or solar water purification products for practical use.

UV/VIS Characterization and FT-IR Analysis of Harmattan Dust across Sub-Sahara Region of Africa

Abstract: The suspended dust particles that blow across Nigeria as a result of north-east trade wind emanating from the Sahara desert annually are locally referred to as Harmattan. Suspended dust samples were collected across ten different stations in Nigeria; namely: Maiduguri (11º49'N, 13º09'E), Potiskum (11º43'N, 11º02'E), Bauchi (10º17'N, 09º 48'E), Jos (9º55'N, 8º55'E), Lafia (08º49'N, 07º50'E), Abuja (09º09'N, 07º11'E), Minna (9º36'N, 06º35'E), Ilorin (8º36'N, 4º 35'E), Oyo (8º12'N, 3º42'E) and Iwo (7º63'N, 4º19'E) and analyzed using Fourier Transform Infrared (FT-IR) and UV-Visible spectroscopy. The quantitative, qualitative and optical characterization analyses were carried out on all the samples collected across all the stations considered, in order to obtain the functional groups and some elements present in the samples. The FT-IR spectra peaks show that the transmittance waveband from 3337.8 cm-1 to 3291.2 cm-1 corresponds to the Hydroxyl group, H-bonded OH stretch in plane and out of plane bonds for all the stations considered. These bonds represent the presence of transition metals and unsaturated bonds found in the samples, which include K, Ca, Ti, Mn, Fe, Ni, Cu, Zn, Mo, As, Zr, Pb, V, Sr, Cr and Ce. The samples collected across all stations have maximum UV absorbance peaks at around 210 nm waveband and weak visible light absorbance peaks (orange – red spectra) around 620 nm and 700 nm. The study concluded that the transmittance waveband, the waveband absorbance peaks and the elemental composition of the dust samples analyzed vary from station to station. This study will however recommend that further study be made for the purpose of environmental awareness. Keywords: Harmattan, Particles, FT-IR, UV, Dust.

A two-dimensional MoS2/SnS heterostructure for promising photocatalytic performance: First-principles investigations

MoS 2 -based two-dimensional (2D) heterostructure photocatalysts have attracted increasing attention due to their prominent photocatalytic performance, but still suffer from weak visible light absorption and low solar-to-hydrogen conversion efficiency. Herein, we comprehensively investigate the structural and electronic properties of 2D MoS 2 /SnS heterostructure using first-principles calculations. It is found that the MoS 2 /SnS heterostructure is a stable interface and forms a type-II heterojunction , which definitely facilitates the spatial separation and migration of photoexcited electron-hole pairs under light irradiation. More importantly, a relatively small band gap (roughly 0.29 eV) enables its light absorption spectrum to cover the entire visible light region. Interestingly, the Mo atoms in the MoS 2 /SnS heterostructure would turn into catalytic active sites. As a result, constructing heterostructure of MoS 2 with SnS improves light absorption, accelerates the separation of electron-hole pairs, and activates the Mo atom at the basal plane, all of which could be beneficial to the photocatalytic activity . These results provide monolayer MoS 2 -based heterojunction photocatalysts and insightful understanding of their physical mechanism. • The MoS 2 /SnS heterostructure is a stable interface and forms a type-II heterojunction. • The type-II heterojunction facilitates the spatial separation and migration of electron-hole pairs under light irradiation. • Small band gap enables its light absorption spectrum to cover the entire visible light region. • The Mo atoms in the MoS 2 /SnS heterostructure would turn into catalytic active sites.

Bandgap Engineering of Lead-Free Double Perovskite Cs2AgInCl6 Nanocrystals via Cu2+-Doping

Lead-free double perovskites (DPs) with excellent moisture, light, and heat stability have been explored as alternatives to toxic lead halide perovskite (APbX3) (A for monovalent cation and X for Cl, Br, or I). However, the bandgaps of the current DPs are generally larger and either indirect or direct forbidden, which leads to weak visible light absorption and limitation for photovoltaic and other optoelectronic applications. Herein, we demonstrate the first synthesis of Cu2+-doped Cs2AgInCl6 double perovskite nanocrystals via a facile hot-injection solution approach. The electronic bandgap can be dramatically tuned from ∼3.60 eV (Cs2AgInCl6, parent) to ∼2.19 eV (Cu2+-doped Cs2AgInCl6) by varying the Cu2+ doping amount. We conclude that the decrease of bandgap is attributed to the overlap of the Ag-d/In-p/Cl-p orbitals and the Cu-3d orbitals in the valence band. The wide tunability of the optical and electronic properties makes Cu2+-Doped Cs2AgInCl6 DP NCs promising candidates for future optoelectronic device applications.

Photo-induced antifouling polyvinylidene fluoride ultrafiltration membrane driven by weak visible light

To enhance the performance of ultrafiltration membranes, a polyvinylidene fluoride (PVDF) blending membrane with photo-induced antifouling performance was fabricated. La3+- and Yb3+-doped titanium dioxide-reduced graphene oxide (TiO2-RGO) composites were initially prepared by adsorption-phase synthesis coupled with solvothermal reduction. The doped TiO2-RGO composites were then blended with the PVDF materials. The results showed that adding well-distributed, doped, and hydrophilic TiO2-RGO improved the pore structures and surface polarity of the blending membranes, thus improving their permeation and antifouling performance. After addition of doped TiO2-RGO with photocatalytic activity, the antifouling performance of the resulting blending membranes increased under weak visible-light irradiation. The agglomerated doped TiO2-RGO in the polymeric matrix reduced the hydrophilicity and porosity of the resulting membranes, thereby decreasing their water permeability and antifouling performance. Solvothermal reduction through ethylene glycol also improved the photocatalytic activity of Yb-doped TiO2-RGO and enhanced the affinity between doped TiO2-RGO and PVDF. These two effects simultaneously increased the water permeability and photo-induced antifouling performance of the blending membranes. The flux recovery rate of the blending membranes containing Yb-doped TiO2-RGO treated by ethylene glycol exceeded 69% after illumination. In particular, the flux recovery rate of membranes reached about 96% after illumination coupling with washing.

Semitransparent Organic Solar Cells Enabled by a Sequentially Deposited Bilayer Structure.

Semitransparent organic solar cells (ST-OSCs) have been regarded as a promising candidate for building integrated photovoltaics. In general, most of the ST-OSCs are based on a bulk heterojunction (BHJ) structure in which the morphology of the BHJ film must be delicately optimized. In this work, we introduce a sequentially deposited bilayer structure into ST-OSCs by using a PTB7-Th/IEICO-4F combination. The adoption of the bilayer structure not only simplifies the device optimization, but it is also found that, as the donor and the acceptor are separately deposited, the power conversion efficiency (PCE) of bilayer ST-OSCs can be improved by simply increasing the thickness of IEICO-4F, which has strong near infrared absorption but weak visible light absorption, without significantly affecting the average visible light transmittance (AVT) of the device. However, in the BHJ structure, the increase in BHJ film thickness unavoidably enhances the donor absorption in the visible light region, leading to a tradeoff between the PCE and AVT in BHJ-structured ST-OSCs. Eventually, the bilayer-structured device exhibits a better overall performance than the BHJ-structured device, e.g., a PCE of 8.5% for the bilayer structure versus a PCE of 8.1% for the BHJ structure with an AVT around 21%. Our findings indicate that the sequentially deposited bilayer structure, aside from its easy processing characteristics, also has great potential for preparing high-performance ST-OSCs.

Synthesis of three-component C3N4/rGO/C-TiO2 photocatalyst with enhanced visible-light responsive photocatalytic deNOx activity

In order to realize high efficiency photocatalysis deNOx effect, a homogeneous three-component photocatalyst, C3N4/rGO/C-TiO2 was successfully synthesized by an in situ synthesis method. First, C3N4/rGO composite was prepared to increase the contact surface between them. Then, C-TiO2 was crystallized on the surface of the C3N4/rGO to obtain relatively dispersed C-TiO2 nanoparticles on the C3N4/rGO. The as-prepared photocatalyst was evaluated by NO removal ratio under weak visible and UV LED light irradiation. C3N4/rGO/C-TiO2 was compared with sample prepared by simple mixing of C3N4, rGO and C-TiO2 within a solution. As a result, sample prepared by in situ synthesis exhibited the highest photocatalytic activity, together with high apparent quantum efficiency. The transient absorption measurement clarified that the composite photocatalyst possessed longer carrier lifetime if compared to that of each component material, resulted to its higher photocatalytic activity. The three-component photocatalyst is thought to have shown enhancement in photocatalytic activity by Z-scheme mechanism with rGO as an electron mediator to improve the performance of Z-scheme.

Modification and functional investigation of self-assembled two-dimensional TiO2 nanosheets with abundant hydroxyl groups

Self-assembled two-dimensional (2D) TiO2 nanosheets are only excited under UV light. They suffer from weak visible light absorption and fast recombination of photogenerated electron-holes carriers. In this paper, four kinds of functionalized modifications were realized through complexing self-assembled 2D TiO2 nanosheets with Fe3O4 nanoparticles, Fe2O3 nanoparticles, N doping, and combining with carbon quantum dots due to the large amount of hydroxyl groups present on the surface of the nanosheet, thereby forming the TiO2/Fe3O4, TiO2/Fe2O3, N-doped TiO2, and TiO2/C composites. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and X-ray photoelectron spectroscopy (XPS) were used to characterize the synthesized products, confirming the successful synthesis of self-assembled 2D TiO2-based composites. By modification, the increasingly improved photocatalytic properties of self-assembled 2D TiO2 nanosheets are also presented. These findings may open up a new avenue and stimulate further research to prepare more self-assembled 2D TiO2-based composites.