Article

Piezotronic Effect-Augmented Cu 2– x O–BaTiO 3 Sonosensitizers for Multifunctional Cancer Dynamic Therapy

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Abstract

Ultrasound (US)-triggered sonodynamic therapy (SDT) based on semiconductor nanomaterials has attracted considerable attention for cancer therapy. However, most inorganic sonosensitizers suffer from low efficiency due to the rapid recombination of electron-hole pairs. Herein, the Cu2-xO-BaTiO3 piezoelectric heterostructure was fabricated as a sonosensitizer and chemodynamic agent, simultaneously, for improving reactive oxygen species (ROS) generation and cancer therapeutic outcome. Under US irradiation, the Cu2-xO-BaTiO3 heterojunction with a piezotronic effect exhibits high-performance singlet oxygen (1O2) and hydroxyl radical (•OH) generation to enhance SDT. Moreover, it possesses Fenton-like reaction activity to convert endogenous H2O2 into •OH for chemodynamic therapy (CDT). The integration of SDT and CDT substantially boosts ROS generation and cellular mitochondria damage, and the in vitro and in vivo results demonstrate high cytotoxicity and tumor inhibition on murine refractory breast cancer. This work realizes improvement in cancer therapy using piezoelectric heterostructures with piezotronic effects.

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Ferroelectric materials have drawn widespread attention due to their switchable spontaneous polarization and anomalous photovoltaic effect. The coupling between ferroelectricity and the piezo-phototronic effect may lead to the design of distinctive photoelectric devices with multifunctional features. Here, we report an enhancement of the photovoltaic performances in the ferroelectric p-type La-doped bismuth ferrite film (BLFO)/ n-type zinc oxide (ZnO) nanowire arrays heterojunction, by rationally coupling the strain-induced piezoelectricity in ZnO nanowires and the ferroelectricity in BLFO. Under a compressive strain of -2.3% and a 10 V upward poling of the BLFO, the open-circuit voltage (VOC) and short-circuit current density (JSC) of the device increase by 8.4% and 54.7%, respectively. Meanwhile, the rise (/decay) time is modulated from 153.7 (/108.8) to 61.28 (/74.86) ms. Systematical band diagram analysis reveal that the promotion of photo-generated carriers and boost of the photovoltaic performances of the device can be attributed to the modulated carrier transport behaviors at the BLFO/ZnO interface and the superposed driving forces arising from the adding up of the piezoelectric potential and ferroelectric polarization. In addition, COMSOL simulation results of piezopotential distribution in ZnO nanowire arrays and the energy band structure change of the heterojunction further confirm the mechanisms. This work not only presents an approach to design high-performance ferroelectric photovoltaic devices, but also further broadens the research scope of piezo-phototronics.
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The emergence of hydroxyl radical (•OH)−mediated chemodynamic therapy (CDT) by Fenton or Fenton−like reaction holds great potential for improving anticancer efficacy. Herein, an activatable autocatalytic nanoreactor (HT@GOx−DMONs) was developed for self−boosted Fenton−like CDT via decorating Cu2+−based metal−organic framework (MOF) on glucose oxidase (GOx)−loaded dendritic mesoporous organosilica nanoparticles (DMONs) for the first time. The obtained nanoreactor could prevent the premature leakage of Cu2+ and GOx in neutral physiological environments conducted by the gatekeeper of growing carboxylate MOF (HKUST−1), but the explosive release of agents could be realized due to the activated degradation of external HKUST−1 in acidic condition of endo/lysosomes, which thereby endowed this nanoreactor with the performance of pH−triggered •OH generation driven by Cu+−mediated autocatalytic Fenton−like reaction. Excitingly, Cu2+−induced glutathione (GSH) depletion and GOx−catalyzed H2O2 self−sufficiency unlocked by acid dramatically enhanced •OH generation. As expected, the effect of self−amplified CDT based on Cu2+−containing HT@GOx−DMONs presented wonderful in vitro toxicity and in vivo antitumor ability without leading to the significant side−effects. This autocatalytic Fenton−like nanoreactor with GSH consumption and self−supplying H2O2 in response to acid may provide a promising paradigm for on−demand violent CDT.
Article
Ultrasound (US) assisted oncotherapy has aroused extensive attention due to its capacities to conquer significant restrictions covering short tissue penetration depth and high phototoxicity in photo-induced therapy. We herein developed a class of pure phase perovskite-type bimetallic oxide, namely bismuth ferrite nanocatalysts (BFO NCs), for multimodality imaging-guided and US-enhanced chemodynamic therapy (CDT) against malignant tumor. As-prepared BFO nanoparticles with poly(ethylene glycol)-grafted phosphorylated serine (pS-PEG) modification exhibit satisfactory physiological stability and biocompatibility. The BFO NCs also present high fluorescence emission within the second near-infrared region when irradiated upon 808 nm laser. Intriguingly, the BFO NCs demonstrate highly efficient US-enhanced generation of hydroxyl free radicals, as the cavitation bubbles produced by US trigger partial grievous turbulence and promote the transfer rate of the Fenton reagents. Thus, the BFO NCs enable effective inhibition of tumor growth assisted with external US, and the treatment efficacy can be monitored by computer tomography, magnetic resonance and fluorescence imaging. Meanwhile, H2O2 and US, as double logic gate, activate the BFO NCs to trigger the iron-catalyzed and US-enhanced CDT with high specificity and treatment efficiency. Therefore, the BFO NCs as a theranostic agent with an enhanced chemodynamic therapeutic effect assisted with external US and a multimodality imaging capacity are put forward, which show a promising prospect for noninvasive chemodynamic oncotherapy.
Article
Current photocatalytic semiconductors often have low catalytic performance due to limited light utilization and fast charge carrier recombination. Formation of Schottky junction between semiconductors and plasmonic metals can broaden the light absorption and facilitate the photon‐generated carriers separation. To further amplify the catalytic performance, herein, an asymmetric gold‐zinc oxide (Asy‐Au−ZnO) nanorod array is rationally designed, which realizes the synergy of piezocatalysis and photocatalysis, as well as spatially oriented electron−hole pairs separation, generating a significantly enhanced catalytic performance. In addition to conventional properties from noble metal/semiconductor Schottky junction, the rationally designed heterostructure has several additional advantages: 1) The piezoelectric ZnO under light and mechanical stress can directly generate charge carriers; 2) the Schottky barrier can be reduced by ZnO piezopotential to enhance the injection efficiency of hot electrons from Au nanoparticles to ZnO; 3) the unique asymmetric nanorod array structure can achieve a spatially directed separation and migration of the photon‐generated carriers. When ultrasound and all‐spectrum light irradiation are exerted simultaneously, the Asy‐Au−ZnO reaches the highest catalytic efficiency of 95% in 75 min for dye degradation. It paves a new pathway for designing unique asymmetric nanostructures with the synergy of photocatalysis and piezocatalysis. An asymmetric Au−ZnO nanorod array is developed for efficient separation of photon‐generated charge carriers with assistance of piezophototronic effect. The unique asymmetric structure can significantly enhance the spatially directed migration and separation of the photon‐generated carriers with assistance of piezophototronic effect, and further realize enhanced catalytic activity by the synergy of piezocatalysis and photocatalysis.
Article
A group of copper complexes supported by polydentate pyridylamide ligands H2bpda and H2ppda were synthesized and characterized. The two Cu(II) dimers [CuII2(Hbpda)2(ClO4)2] (1) and [CuII2(ppda)2(DMF)2] (2) were constructed by using neutral ligands to react with Cu(II) salts. Although the dimers showed similar structural features, the second-sphere interactions affect the structures differently. With the application of Et3N, the tetranuclear cluster (HNEt3)[CuII4(bpda)2(μ3-OH)2(ClO4)(DMF)3](ClO4)2 (3) and hexanuclear cluster (HNEt3)2[CuII6(ppda)6(H2O)2(CH3OH)2](ClO4)2 (4) were prepared under similar reaction conditions. The symmetrical and unsymmetrical arrangement of the ligand donors in ligands H2bpda and H2ppda led to the dramatic conformation difference of the two Cu(II) complexes. As part of our effort to explore mixed-valence copper chemistry, the triple-decker pentanuclear cluster [CuII3CuI2(bpda)3(μ3-O)] (5) was prepared. XPS examination demonstrated the localized mixed-valence properties of complex 5. Magnetic studies of the clusters with EPR evidence showed either weak ferromagnetic or antiferromagnetic interactions among copper centers. Due to the trigonal-planar conformation of the trinuclear Cu(II) motif with the μ3-O center, complex 5 exhibits geometric spin frustration and engages in antisymmetric exchange interactions. DFT calculations were also performed to better interpret spectroscopic evidence and understand the electronic structures, especially the mixed-valence nature of complex 5.
Article
Direct conversion of solar light into chemical energy by means of photocatalysis or photoelectrocatalysis is currently a point of focus for sustainable energy development and environmental remediation. However, its current efficiency is still far from satisfying, suffering especially from severe charge recombination. To solve this problem, the piezo‐phototronic effect has emerged as one of the most effective strategies for photo(electro)catalysis. Through the integration of piezoelectricity, photoexcitation, and semiconductor properties, the built‐in electric field by mechanical stimulation induced polarization can serve as a flexible autovalve to modulate the charge‐transfer pathway and facilitate carrier separation both in the bulk phase and at the surfaces of semiconductors. This review focuses on illustrating the trends and impacts of research based on piezo‐enhanced photocatalytic reactions. The fundamental mechanisms of piezo‐phototronics modulated band bending and charge migration are highlighted. Through comparing and classifying different categories of piezo‐photocatalysts (like the typical ZnO, MoS2, and BaTiO3), the recent advances in polarization‐promoted photo(electro)catalytic processes involving water splitting and pollutant degradation are overviewed. Meanwhile the optimization methods to promote their catalytic activities are described. Finally, the outlook for future development of polarization‐enhanced strategies is presented. The piezo‐phototronic effect enables the engineering of charge‐carrier characteristics at both heterojunction interfaces and the bulk phase, and provides a driving force for the transport of photoinduced charges in specific directions. This review focuses on the advanced polarization‐promoted processes involving water splitting and pollutant degradation.
Article
Ferroptosis, a newfound non-apoptotic cell death pathway, results from the accumulation of iron-dependent lipid peroxide (LPO). Recently, emerging iron-based nanomaterials have been extensively developed to induce Fenton reaction-dependent ferroptosis for cancer therapy. However, insufficient amount of H2O2 and limited acidity of tumor could not satisfy the optimal conditions for Fenton reaction, which extremely limited the efficacy of ferroptosis therapy. Herein, we report a novel glutathione (GSH) and iron redox couple sequentially triggered LPO generator (LPOgener) which can directly supply the Fenton reaction-independent downstream executioner of ferroptosis for cancer therapy. By harnessing GSH-mediated Fe3+ reduction and the well-established iron redox couple-mediated lipid peroxidation, LPOgener was constructed by complete ferric ammonium citrate (FAC) and unsaturated lipids-rich phosphatidylcholine, and formed as FAC loaded liposome. The Fe3+ encapsulated in LPOgener could be efficiently reduced to Fe2+ under high GSH level in tumor cells. Subsequently, the formed iron redox couple could trigger overwhelming lipid peroxidation for Fenton reaction-independent ferroptosis. Superior anticancer therapeutic effect with little systemic toxicity demonstrated that LPOgener was a potent ferroptosis-inducing agent for cancer therapy. Therefore, to directly supply the druglike, easily prepared, GSH and iron redox couple sequentially triggered LPOgener would provide a new direction in designing strategies for ferroptosis therapy.
Article
Sonodynamic therapy eliminates cancer cells with reactive oxygen species (ROS) triggered by ultrasound whose energy is spatiotemporally controllable, safe to human tissues and organs, and deeply penetrating through tissues. Its application, however, is hindered by the scarcity of sonodynamic sensitizers. We herein demonstrate piezoelectric materials as a new source of sonodynamic sensitizers, using few-layer black phosphorous (BP) nanosheet as a model. BP nanosheet exhibited ultrasound-excited cytotoxicity to cancer cells via ROS generation, thereby suppressing tumor growth and metastasis without causing off-target toxicity in tumor-bearing mouse models. The ultrasonic wave introduces mechanical strain to BP nanosheet, leading to piezoelectric polarization which shifts the conduction band of BP more negative than O2/•O2− while its valance band more positive than H2O/•OH, thereby accelerating the ROS production. This work identifies a new mechanism for discovering sonodynamic sensitizers and suggests BP nanosheet as an excellent sensitizer for tumor sonodynamic therapy.
Article
Carbon nanomaterial-based cancer therapy has flourished for decades. However, their practical applications on clinical bases still pose a challenge to address the dilemma of metabolism in vivo. In this study, an attempt is made to design a degradable carbon–silica nanocomposite (CSN) with immunoadjuvant property, which could undergo an enzyme-free degradation process into small particles (~5 nm) and facilitate its clinical application. CSN harbors photothermal and photodynamic properties, and meanwhile as an immunoadjuvant, would help to generate the tumor-associated antigens and mature dendritic cells (DCs). Potent antitumor effects have been achieved in both 4T1 and patient-derived xenograft (PDX) tumor models with tumor inhibition efficiencies of 93.2% and 92.5%, respectively. We believe that this strategy will benefit to the possible clinical translation and carbon–silica nanomaterial-based cancer therapy.
Article
Photosynthesis with Z-scheme charge transfer has been recognized as an efficient pathway to achieve solar-energy conversion. Herein, the all-solid-state direct Z-scheme ZnO-WO3-x nanorod arrays were synthesized by in-situ solvothermal treatment for highly piezoelectric (PE)-photoelectrochemical (PEC) water splitting. The chemical bonding between WO3-x and ZnO via W-O-Zn and the inherent band structures/Fermi levels drive the formation of direct Z-scheme charge-transfer pathway. Importantly, the optimized structure (Zn-W-5) shows higher PEC activities with high photocurrent density of 2.39 mA/cm² at 1.23 V vs. RHE, which is 2.13 times higher than pure ZnO. Surprisingly, the obvious PE polarization of ZnO increases its Fermi level toward conduction band and significantly enhances Z-scheme effect between ZnO and WO3-x. Especially, the best sample (Zn-W-5-1000 rpm) shows a photocurrent of 3.38 mA/cm² at 1.23 V vs. RHE, which is 3.02 times higher than pure ZnO. This work provides a facile PE polarization approach for enhancement of Z-scheme charge-transfer process.
Article
The integration of reactive oxygen species (ROS)-involved photodynamic therapy (PDT) and chemodynamic therapy (CDT) holds great promise for enhanced anticancer effects. Herein, we report biodegradable cancer cell membrane-coated mesoporous copper/manganese silicate nanospheres (mCMSNs) with homotypic targeting ability to the cancer cell lines and enhanced ROS generation through singlet oxygen (1O2) production and glutathione (GSH)-activated Fenton reaction, showing excellent CDT/PDT synergistic therapeutic effects. We demonstrate that mCMSNs are able to relieve the tumor hypoxia microenvironment by catalytic decomposition of endogenous H2O2 to O2 and further react with O2 to produce toxic 1O2 with a 635 nm laser irradiation. GSH-triggered mCMSNs biodegradation can simultaneously generate Fenton-like Cu+ and Mn2+ ions and deplete GSH for efficient hydroxyl radical (•OH) production. The specific recognition and homotypic targeting ability to the cancer cells were also revealed. Notably, relieving hypoxia and GSH depletion disrupts the tumor microenvironment (TME) and cellular antioxidant defense system, achieving exceptional cancer-targeting therapeutic effects in vitro and in vivo. The cancer cells growth was significantly inhibited. Moreover, the released Mn2+ can also act as an advanced contrast agent for cancer magnetic resonance imaging (MRI). Thus, together with photosensitizers, Fenton agent provider and MRI contrast effects along with the modulating of the TME allow mCMSNs to realize MRI-monitored enhanced CDT/PDT synergistic therapy. It provides a paradigm to rationally design TME-responsive and ROS-involved therapeutic strategies based on a single polymetallic silicate nanomaterial with enhanced anticancer effects.
Article
Reactive oxygen species (ROS) play an essential role in regulating various physiological functions of living organisms. The intrinsic biochemical properties of ROS, which underlie the mechanisms necessary for the growth, fitness, or aging of living organisms, have been driving researchers to take full advantage of these active chemical species for contributing to medical advances. Thanks to the remarkable advances in nanotechnology, great varieties of nanomaterials with unique ROS-regulating properties have been explored to guide the temporospatial dynamic behaviors of ROS in biological milieu, which contributes to the emergence of a new-generation therapeutic methodology, i.e., nanomaterial-guided in vivo ROS evolution for therapy. The interdependent relationship between ROS and their corresponding chemistry, biology, and nanotherapy leads us to propose the concept of "ROS science", which is believed to be an emerging scientific discipline that studies the chemical mechanisms, biological effects, and nanotherapeutic applications of ROS. In this review, state-of-art studies concerning recent progresses on ROS-based nanotherapies have been summarized in detail, with an emphasis on underlying material chemistry of nanomaterials by which ROS are generated or scavenged for improved therapeutic outcomes. Furthermore, key scientific issues in the evolution of ROS-based cross-disciplinary fields have also been discussed, aiming to unlock the innate powers of ROS for optimized therapeutic efficacies. We expect that our demonstration on this evolving field will be beneficial to the further development of ROS-based fundamental researches and clinical applications.
Article
In this study, we report a remarkably active CeVO4 nanozyme that functionally mimics cytochrome c oxidase (CcO), the terminal enzyme in the respiratory electron transport chain, by catalyzing a four‐electron reduction of dioxygen to water. The nanozyme catalyzes the reaction by using cytochrome c, the biological electron donor for CcO, at physiologically relevant pH. The CcO activity of the CeVO4 nanozymes depends on the relative ratio of surface Ce3+/Ce4+ ions, the presence of V5+ and the surface‐Cyt c interactions. The complete reduction of oxygen to water takes place without release of any partially reduced oxygen species (PROS) such as superoxide, peroxide and hydroxyl radicals.
Article
Piezoelectric materials produce electricity when strained, making them ideal for different types of sensing applications. The most effective piezoelectric materials are ceramic solid solutions in which the piezoelectric effect is optimized at what are termed morphotropic phase boundaries (MPBs). Ceramics are not ideal for a variety of applications owing to some of their mechanical properties. We synthesized piezoelectric materials from a molecular perovskite (TMFM) x (TMCM) 1–x CdCl 3 solid solution (TMFM, trimethylfluoromethyl ammonium; TMCM, trimethylchloromethyl ammonium, 0 ≤ x ≤ 1), in which the MPB exists between monoclinic and hexagonal phases. We found a composition for which the piezoelectric coefficient d33 is ~1540 picocoulombs per newton, comparable to high-performance piezoelectric ceramics. The material has potential applications for wearable piezoelectric devices.
Article
There are acknowledged risks of metastasis of cancer cells and obstructing cancer treatment from hypoxia. In this work, we design a multifunctional nanocomposite for treating hypoxia based on the oxygen release capability of CuO triggered by microwave (MW). Core-shell CuO@ZrO2 nanocomposites are prepared by confining CuO nanoparticles within the cavities of mesoporous ZrO2 hollow nanospheres. The 1-butyl-3-methylimidazolium hexafluorophosphate (IL) is loaded to the CuO@ZrO2 nanocomposites for improving microwave thermal therapy (MWTT). 1-Tetradecanol (PCM) is introduced to regulate the release of chemotherapeutic drugs of Doxorubicin (DOX). Thus, the IL-DOX-PCM-CuO@ZrO2 multifunctional (IDPC@Zr) nanocomposites are obtained. Finally, IDPC@Zr nanocomposites are modified by monomethoxy polyethylene glycol sulfhydryl (mPEG-SH, 5kDa) (IDPC@Zr-PEG nanocomposites). IDPC@Zr-PEG nanocomposites can produce oxygen in the tumor microenvironment during the course of tumor treatment, thereby alleviating the hypoxic state and improving the therapeutic effect. In vivo anti-tumor experiments prove that the tumor rate is very high and the inhibition rate is 92.14%. In addition, CT imaging contrast of the nanocomposites can be enhanced due to the high atomic number of Zr. Therefore, IDPC@Zr-PEG nanocomposites can be applied for monitoring the tumor treatment process in real time. The combined therapy offers many opportunities, such as the production of oxygen from CuO nanoparticles by MW to alleviate hypoxia, the enhancement of combined treatment of MWTT and chemotherapy, and the potential application of CT imaging to visualize the treatment process, which therefore provides a promising method for clinical treatment of tumors in the future.
Article
Therapeutic nanosystems which can be triggered by the distinctive tumor microenvironment possess great selectivity and safety to treat cancers via in situ transformation of nontoxic prodrugs into toxic therapeutic agents. Here, we constructed an intelligent, magnetic targeting and tumor microenvironment responsive nanocatalysts that can acquire oxidation therapy of cancer via specific reaction at tumor site. The magnetic nanoparticle core of iron carbide-glucose oxidase (Fe5C2-GOD) achieved by physical absorption has a high enzyme payload and the manganese dioxide (MnO2) nanoshell as an intelligent “gatekeeper” shields GOD from premature leaking until reaching tumor tissue. Fe5C2-GOD@MnO2 nanocatalysts maintained inactive in normal cells upon systemic administration. On the contrary, after endocytosis by tumor cells, tumor acidic microenvironment induced decomposition of MnO2 nanoshell into Mn2+ and O2, meanwhile, released GOD. Mn2+ could serve as magnetic resonance imaging (MRI) contrast agent for real-time monitoring treatment process. Then the generated O2 and released GOD in nanocatalysts could effectively exhaust glucose in tumor cells, simultaneously, generate plenty of H2O2 which may accelerate the subsequent Fenton reaction catalyzed by Fe5C2 magnetic core in mild acidic tumor microenvironment. Finally, we demonstrated the tumor site-specific production of highly toxic hydroxyl radicals for enhanced anticancer therapeutic efficacy but minimized systemic toxicity in mice.
Article
The introduction of piezoelectric field has been proven a promising method to enhance photocatalytic activity by preventing photoelectron-hole recombination. However, the formation of piezoelectric field requires additional mechanical force or high-frequency ultrasonic baths, which limits its potential application in industrial scale. Therefore, it is of great practical significance to design the catalyst which can harvest the discrete energy such as the fluid mechanical energy to form the electric field. Herein, PZT/TiO2 catalyst with a core-shell configuration was prepared by a simple coating method. By collecting the mechanical energy of water, an internal piezoelectric field was induced. Under 800 rpm stirring, transient photocurrent measured on PZT/TiO2 electrode is about 2.7 times higher than that of 400 rpm. Correspondingly, the photocatalytic degradation rate and mineralization efficiency of RhB, BPA, phenol, p-chlorophenol much improved, showing the promoting effect of piezoelectric field generated directly from harvesting the discrete fluid mechanical energy.
Article
Bacteria induced infectious diseases have threated the lives and health of millions people each year. Nanosized titanium dioxide (TiO2) have been developed for photodynamic bacterial killing with minimal drug resistance, but the efficiency was restricted by their large band gap, limited light-absorption region, and rapid electron-hole recombination. In this work, we rationally fabricated a TiO2/BTO/Au multilayered coaxial heterostructured nanorod array by inserting a ferroelectric semiconductor barium titanate (BaTiO3) nanolayer between TiO2 nanorod and gold nanoparticles (AuNPs). The TiO2/BTO/Au heterostructure showed greatly enhanced reactive oxygen species (ROS) (superoxide (O2•⁻) and hydroxyl radicals (•OH)) generation, and incident photo-electron conversion efficiency (IPCE) in UV/visible light region. On the basis of experimental observations, the detailed photodynamic mechanism of the enhanced ROS generation was proposed, mainly ascribed to the piezophototronic effect and plasmonic property of the nanorod array. The nanorod array was used as an antibacterial coating to kill gram-negative bacterium E. coli and gram-positive bacterium S. Aureus with an antibacterial efficiency up to 99.9% under simulated sunlight. It also showed an efficient promotion of infectious wound regeneration in mice with S. aureus infected dermal wounds.
Article
Engineering the multi-heterojunction in semiconductor photocatalysts have been considered as a promising tactics to achieve highly-efficient photocatalytic solar-fuels generation, because the photoinduced hetero-interfacial charge transfer can greatly hinder the recombination process of charge-carrier in photocatalysts. In this work, we fabricated copper species nanocrystals/TiO2 multi-heterojunction photocatalysts through in-situ reduction of CuO nanocrystals in CuO/TiO2 electrospun nanofibers by using a glucose-assisted hydrothermal process. By changing the concentration of glucose, the composition ratio of copper species nanocrystals, including CuO, Cu2O, and Cu, can be adjusted in multi-heterojunction nanofibers. Upon simulated sunlight irradiation, the optimal copper species nanocrystals/TiO2 multi-heterojunction nanofibers exhibited the H2 evolution rate of ∼10.04 mol h-1, which is 17.3 times higher than that of bare TiO2 nanofibers (~0.57 mol h-1).
Article
The detection methods and generation mechanisms of the intrinsic reactive oxygen species (ROS), i.e., superoxide anion radical (•O2–), hydrogen peroxide (H2O2), singlet oxygen (¹O2), and hydroxyl radical (•OH) in photocatalysis, were surveyed comprehensively. Consequently, the major photocatalyst used in heterogeneous photocatalytic systems was found to be TiO2. However, besides TiO2 some representative photocatalysts were also involved in the discussion. Among the various issues we focused on the detection methods and generation reactions of ROS in the aqueous suspensions of photocatalysts. On the careful account of the experimental results presented so far, we proposed the following apprehension: adsorbed •OH could be regarded as trapped holes, which are involved in a rapid adsorption–desorption equilibrium at the TiO2–solution interface. Because the equilibrium shifts to the adsorption side, trapped holes must be actually the dominant oxidation species whereas •OH in solution would exert the reactivity mainly for nonadsorbed reactants. The most probable routes of generating intrinsic ROS at the surfaces of two polymorphs of TiO2, anatase and rutile, were discussed along with some plausible rational reaction processes. In addition to the four major ROS, three ROS, that is organic peroxides, ozone, and nitric oxide, which are less common in photocatalysis are also briefly reviewed.
Article
Photocatalytic hydrogen evolution is a potential route for converting inexhaustible solar energy into available clean chemical energy. Herein, highly efficient and stable Cu2(OH)2CO3/TiO2 photocatalysts for hydrogen generation are prepared by incorporating Cu2(OH)2CO3 clusters onto the surface of TiO2 through a facile precipitation method. The obtained Cu2(OH)2CO3/TiO2 photocatalyst with optimal Cu2(OH)2CO3 content of 0.5 mol% shows an outstanding photocatalytic H2-production rate of 6713 μmol h⁻¹ g⁻¹ (with apparent quantum efficiency of 15.4% at 365 nm), which is comparable to the excellent Pt/TiO2 photocatalyst and more efficient than other copper specie modified TiO2 photocatalyst. The formation of Cu2(OH)2CO3/Cu⁺/Cu⁰⁰ clusters essentially contribute to the enhanced H2-production activity by reducing the over-potential of water reduction and promoting the transfer of photogenerated electrons from the conduction band of TiO2 to the Cu2(OH)2CO3/Cu⁺/Cu⁰⁰ clusters. A high stability of the Cu2(OH)2CO3/TiO2 photocatalyst is achieved due to the re-oxidation process of Cu⁺/Cu⁰⁰ to Cu2(OH)2CO3 and structure confinement of Cu2(OH)2CO3 clusters in the mesopores of TiO2. This work brings in new insight in developing low-cost noble-metal-free photocatalytic system for solar-to-fuel conversion.