Nanoscale engineering of solid-state materials for boosting hydrogen storage.

The development of novel materials capable of securely storing hydrogen at high volumetric and gravimetric densities is a requirement for the wide-scale usage of hydrogen as an energy carrier. In recent years, great efforts via nanoscale tuning and designing strategies on both physisorbents and chemisorbents have been devoted to improvements in their thermodynamic and kinetic aspects. Increasing the hydrogen storage capacity/density for physisorbents and chemisorbents and improving the dehydrogenation kinetics of hydrides are still considered a challenge. The extensive and fast development of advanced nanotechnologies has fueled a surge in research that presents huge potential in designing solid-state materials to meet the ultimate U.S. Department of Energy capacity targets for onboard light-duty vehicles, material-handling equipments, and portable power applications. Different from the existing literature, in this review, particular attention is paid to the recent advances in nanoscale engineering of solid-state materials for boosting hydrogen storage, especially the nanoscale tuning and designing strategies. We first present a short overview of hydrogen storage mechanisms of nanoscale engineering for boosted hydrogen storage performance on solid-state materials, for example, hydrogen spillover, nanopump effect, nanosize effect, nanocatalysis, and other non-classical hydrogen storage mechanisms. Then, the focus is on recent advancements in nanoscale engineering strategies aimed at enhancing the gravimetric hydrogen storage capacity of porous materials, reducing dehydrogenation temperature and improving reaction kinetics and reversibility of hydrogen desorption/absorption for metal hydrides. Effective nanoscale tuning strategies for enhancing the hydrogen storage performance of porous materials include optimizing surface area and pore volume, fine-tuning nanopore sizes, introducing nanostructure doping, and crafting nanoarchitecture and nanohybrid materials. For metal hydrides, successful strategies involve nanoconfinement, nanosizing, and the incorporation of nanocatalysts. This review further addresses the points to future research directions in the hope of ushering in the practical applications of hydrogen storage materials.

Rational Surface and Interfacial Engineering of IrO2 /TiO2 Nanosheet Arrays toward High-Performance Chlorine Evolution Electrocatalysis and Practical Environmental Remediation.

The chlorine evolution reaction (CER) is a critical and commercially valuable electrochemical reaction in industrial-scale utilization, including the Chlor-alkali industry, seawater electrolysis, and saline wastewater treatment. Aiming at boosting CER electrocatalysis, hybrid IrO2 /TiO2 nanosheet arrays (NSAs) with rational surface and interfacial tuning strategies are proposed in this study. The IrO2 /TiO2 NSAs exhibit superb CER electrocatalytic activity with a low overpotential (44 mV) at 10 mA cm-2 , low Tafel slope of 40 mV dec-1 , high CER selectivity (95.8%), and long-term durability, outperforming most of the existing counterparts. The boosting mechanism is proposed that the aerophobic/hydrophilic surface engineering and interfacial electronic structure tuning of IrO2 /TiO2 are beneficial for the Cl- mass-transfer, Cl2 release, and Volmer-Heyvrosky kinetics during the CER. Practical saline wastewater treatment by using the IrO2 /TiO2 NSAs electrode is further conducted, demonstrating it has a higher p-nitrophenol degradation ratio (95.10% in 60 min) than that of other electrodes. The rational surface and interfacial engineering of IrO2 /TiO2 NSAs can open up a new way to design highly efficient electrocatalysts for industrial application and environmental remediation.

Electrochemical and Photoelectrochemical Water Oxidation for Hydrogen Peroxide Production.

Hydrogen peroxide (H2 O2 ), as a green fuel and oxidant, has drawn increasing attention in the energy and environmental research. Compared with the traditional anthraquinone process, the electrochemical (EC) and photoelectrochemical (PEC) syntheses of H2 O2 are cost-effective and environmentally friendly. In order to construct membraneless EC/PEC devices for the full H2 O2 synthesis, anodic H2 O2 production by water oxidation, which is less developed than cathodic H2 O2 generation, is highly desirable. Here, we review recent developments for the EC/PEC H2 O2 production by water oxidation, including fundamental aspects, benchmarking activity evaluation, material/catalyst selection, and strategies for increasing selectivity, efficiency, and accumulation. Furthermore, we discuss the challenges and outlook of water oxidation for H2 O2 production, especially device-level development, accumulation and stability, and industrial applications. Our review is intended to stimulate studies further improving EC/PEC H2 O2 production.

A review of the α-Fe2O3 (hematite) nanotube structure: recent advances in synthesis, characterization, and applications.

α-Fe2O3 nanotubes are exceptional one-dimensional transition metal oxide materials with low density, large surface area, promising electrochemical and photoelectrochemical properties, which are widely investigated in lithium-ion batteries, photoelectrochemical devices, gas sensors, and catalysis. They have drawn significant attention to the fields of energy storage and conversion, and environmental sensing and remediation due to the increase in the global energy crisis and environmental pollution. Many efforts have been made toward controlling the morphology or impurity doping to improve the intrinsic properties of α-Fe2O3 nanotubes. In this review, we introduce the synthesis methods and physicochemical properties of α-Fe2O3 nanotubes. The fabrication conditions, which are important for the physicochemical properties of materials, are also listed to describe the synthesis processes. Furthermore, the development and breakthrough of various applications in batteries, supercapacitors, photoelectrochemical devices, environmental remediation, and sensors are systematically reviewed. Finally, some of the current challenges and future perspectives for α-Fe2O3 nanotubes are discussed. We believe that this timely and critical mini-review will stimulate extensive studies and attract more attention, further improving the development of the α-Fe2O3 (hematite) nanotube structure.

Fluorinated-functionalized hyaluronic acid nanoparticles for enhanced photodynamic therapy of ocular choroidal melanoma by ameliorating hypoxia.

Photodynamic therapy (PDT) is a method for killing cancer cells by employing reactive singlet oxygen (1O2). However, the inherent hypoxia and oxygen consumption in tumors during PDT lead to a deficient oxygen supply, which in turn hinder the photodynamic efficacy. To overcome this issue, fluorinated-functionalized polysaccharide-based nanocomplexes were prepared by anchoring perfluorocarbons (PFCs) and pyropheophorbide a (Ppa) onto the polymer chains of hyaluronic acid (HA) to deliver O2 in hypoxia area. These amphiphilic conjugates can self-assemble into micelles and its application in PDT is evaluated. Due to the high oxygen affinity of perfluorocarbon segments, and the tumor-targeting nature of HA, the photodynamic effect of the oxygen self-carrying micelles is remarkably enhanced, which is confirmed by increased generation of 1O2 and elevated phototoxicity in vitro and in vivo. These results emphasize the promising potential of polysaccharide-based nanocomplexes for enhanced PDT of Ocular Choroidal Melanoma.

Hydrophilic polyphosphoester-conjugated fluorinated chlorin as an entirely biodegradable nano-photosensitizer for reliable and efficient photodynamic therapy.

An entirely biodegradable nano-photosensitizer platform (PPE-FP2) was fabricated by conjugating the photosensitizer TFPC to hydrophilic polyphosphoesters (PPEs) for efficiently liberating photosensitizers at the tumor site. The complete biodegradability of PPE-FP2 avoided residual nanoparticles in vivo after therapy, realizing reliable and effective photodynamic therapy.

Generation and application of reactive chlorine species by electrochemical process combined with UV irradiation: Synergistic mechanism for enhanced degradation performance.

Saline wastewater originates from many industries, containing a large amount of salt (NaCl) and other toxic and harmful organic matter, which have a great impact on the soil and groundwater. However, the treatment of saline wastewater is a serious problem because organic contents are hard to degrade with the high salinity by the common water treatment technologies. Herein, an electrochemical process coupled with ultraviolet (UV) irradiation was proposed for the saline wastewater treatment. High efficiency of p-nitrophenol (p-NP) and ammonia degradation were contributed from the in situ electrochemical produced active chlorine and photo-induced chlorine radicals. Under the optimal conditions (0.10 A, 0.05 M NaCl, and pH 6.00), approximately 98.91% p-NP was removed after 60 min with the rate constant of 7.521 × 10-2 min-1 in the electrochemical process, and 28.99% mineralization rate was obtained, while with the synergistic effect of UV and electrochemistry, approximately 100% of p-NP removal (k = 9.331 × 10-2 min-1) was achieved by 30 min treatment and about 83.70% of p-NP can be mineralized to CO2 after 60 min. The study on the synergistic mechanism of enhanced degradation performance illustrated that Cl with high oxidation capacity played an important role in the p-NP oxidation. Besides, based on the chlorine radical reactions, this method was also effectively applied to remove ammonia nitrogen (92.00% removal of total nitrogen in 100 min) for nitrogen-containing wastewater. Thus, this study offers a promising approach for the treatment of saline industry wastewater.

In Situ Catalytic Reaction for Solving the Aggregation of Hydrophobic Photosensitizers in Tumor.

The aggregation of hydrophobic photosensitizers limits the therapeutic effect of photodynamic therapy (PDT). Improving the hydrophilicity of photosensitizers can reduce their aggregation for enhancing PDT. Herein, a nanosystem (TPFcNP) is developed by a hydrophobic photosensitizer 5,10,15,20-tetrakis(4-methacryloyloxyphenyl)porphyrin (TMPP) containing multiple carbon-carbon double bonds and a ferrocene-containing amphiphilic block copolymer (PEG-b-PMAEFc), which catalyzes hydrogen peroxide (H2O2) to produce hydroxyl radicals (•OH) in a tumor microenvironment by the Fenton reaction. The •OH could catalyze the addition reaction between the carbon-carbon double bonds of TMPP and overexpressed water-soluble glutathione (GSH) in tumor cells, which greatly improves the hydrophilicity of photosensitizers and reduces their aggregation. Experiments in vitro and in vivo have proved that this strategy significantly enhances the therapeutic efficacy of PDT. Catalyzing intracellular reactions in situ by making use of the tumor microenvironment will open up a new opportunity to solve the aggregation of materials in the tumor for cancer treatment.

Modulation of the lifespan of C. elegans by the controlled release of nitric oxide.

The frontier of nitric oxide biology has gradually shifted from mechanism elucidation to biomanipulation, e.g. cell-proliferation promotion, cell-apoptosis induction, and lifespan modulation. This warrants biocompatible nitric oxide (NO) donating materials, whose NO release is not only controlled by a bioorthogonal trigger, but also self-calibrated allowing real-time monitoring and hence an onset/offset of the NO release. Additionally, the dose of NO release should be facilely adjusted in a large dynamic range; flux and the dose are critical to the biological outcome of NO treatment. Via self-assembly of a PEGylated small-molecule NO donor, we developed novel NO-donating nanoparticles (PEG-NORM), which meet all the aforementioned criteria. We showcased that a low flux of NO induced cell proliferation, while a high flux induced cell oxidative stress and, ultimately, death. Notably, PEG-NORM was capable of efficiently modulating the lifespan of C. elegans. The average lifespan of C. elegans could be fine-tuned to be as short as 15.87 ± 0.29 days with a high dose of NO, or as long as 21.13 ± 0.41 days with a low dose of NO, compared to an average life-span of 18.87 ± 0.46 days. Thus, PEG-NORM has broad potential in cell manipulation and life-span modulation and could drive the advancement of NO biology and medicine.

Self-Amplified Photodynamic Therapy through the 1 O2 -Mediated Internalization of Photosensitizers from a Ppa-Bearing Block Copolymer.

Nanocarriers are employed to deliver photosensitizers for photodynamic therapy (PDT) through the enhanced penetration and retention effect, but disadvantages including the premature leakage and non-selective release of photosensitizers still exist. Herein, we report a 1 O2 -responsive block copolymer (POEGMA-b-P(MAA-co-VSPpaMA) to enhance PDT via the controllable release of photosensitizers. Once nanoparticles formed by the block copolymer have accumulated in a tumor and have been taken up by cancer cells, pyropheophorbide a (Ppa) could be controllably released by singlet oxygen (1 O2 ) generated by light irradiation, enhancing the photosensitization. This was demonstrated by confocal laser scanning microscopy and in vivo fluorescence imaging. The 1 O2 -responsiveness of POEGMA-b-P(MAA-co-VSPpaMA) block copolymer enabled the realization of self-amplified photodynamic therapy by the regulation of Ppa release using NIR illumination. This may provide a new insight into the design of precise PDT.

Sensitization of Hypoxic Tumor to Photodynamic Therapy via Oxygen Self-Supply of Fluorinated Photosensitizers.

Photodynamic therapy (PDT) utilizes photosensitizers to convert innoxious oxygen to cytotoxic reactive oxygen species under an appropriate light, thus inducing cancer cells necrosis. However, PDT performs in an oxygen-dependent method to destroy cells while hypoxia is a feature for most solid tumors. To effectively improve the PDT effect against solid tumors, an oxygen self-supplying and pH-sensitive therapeutic nanoparticle (PTFC) has been developed by the self-assembly of a tetrakis(pentafluorophenyl) chlorin (TFPC)-conjugated block copolymer (POEGMA-b-P(DEAEMA-co-GMA)). PTFC nanoparticles can transport oxygen to a tumor site with their accumulation in the tumor on account of the good oxygen solubility, therefore relieving the oxygen deficiency of a solid tumor and enhancing the PDT efficacy. It is worth noting that the oxygen loading was realized by the fluorinated photosensitizer itself. In addition, the phototoxicity of PTFC nanoparticles is greatly improved in an acidic aqueous environment due to the DEAEMA unit protonation, which not only enhanced the cellular uptake of nanoparticles but also weakened the aggregation of photosensitizers. Taking the hypoxia and acidic microenvironment of solid tumors, PTFC nanoparticles could be efficiently taken up and disassembled to release oxygen upon accumulation at tumor sites, thus significantly improving the PDT efficacy against solid tumors.

GSH-Activatable NIR Nanoplatform with Mitochondria Targeting for Enhancing Tumor-Specific Therapy.

Developing smart photosensitizers that are sensitive to tumor-specific signals for minimal side effects and enhanced antitumor efficacy is a tremendous challenge for tumor phototherapies. Herein, we construct a nanoplatform with glutathione (GSH)-activatable and mitochondria-targeted pro-photosensitizer encapsulated by ultrasensitive pH-responsive polymer for achieving imaging-guided tumor-specific photodynamic therapy (PDT). The GSH-activatable pro-photosensitizer, di-cyanine (DCy7), has been synthesized where two cyanine moieties are covalently conjugated by a disulfide bond, and the hydrophobic DCy7 is further encapsulated with an amphiphilic pH-responsive diblock copolymer POEGMA-b-PDPA to form P@DCy7 nanoparticles. Upon endocytosis by cancer cells, P@DCy7 nanoparticles dissociate at endosome first and then DCy7 is released to cytoplasm and subsequently activated by the high concentration of GSH, finally targets mitochondria for organelle-targeted PDT. Moreover, intracellular antioxidant GSH is consumed during the activation procedure that is beneficial to efficient PDT. These P@DCy7 nanoparticles display selective phototoxicity against tumor cells (HepG2 or 4T1 cells) over normal cells (BEAS-2B cells) in vitro, and their GSH-activatable enhanced PDT efficacy is further confirmed in tumor-bearing mice. Thus, P@DCy7 nanoparticles allow for accurate and highly efficient PDT with minimal side effects, providing an attractive nanoplatform for organelle-targeted precise PDT.

NIR-Triggered "OFF/ON" Photodynamic Therapy through a Upper Critical Solution Temperature Block Copolymer.

Activatable photodynamic therapy (A-PDT) has attracted great attention in precision medicine, which can be activated by endogenous or exogenous stimuli to selectively produce reactive oxygen species (ROS) at the disease site. Thermal responsive polymers with a lower critical solution temperature (LCST) have normally been utilized for constructing A-PDT system. Herein, we fabricated a photothermal activatable photosensitizer (A-PS) by the combination of thermal responsive porphyrin-containing P(AAm-co-AN-co-TPP)-b-POEGMA amphiphilic block copolymer with an upper critical solution temperature (UCST) of 42 °C and a cyanine dye of IR780. The photoactivity of porphyrin units could be severely inhibited by IR780 due to the fluorescence resonance energy transfer (FRET) from TPP to IR780 during blood circulation process ("OFF" state). After an uptake by A549 cells and then irradiated with 808 nm laser, A-PS nanoparticles were subsequently dissociated owing to the increased local temperature above the UCST of the polymer chains by excellent photothermal conversion of IR780, resulting in the enhanced photoactivity of TPP ("ON" state) and the remarkable antitumor effect. Therefore, the UCST-based A-PS extended the biological application of thermal responsive polymers, which may provide a new insight into the design of smart cancer therapeutic systems.

In situ anodic induction of low-valence copper in electro-Fenton system for effective nitrobenzene degradation.

To achieve superior advanced oxidation processes (AOPs), transitional state activators are of great significance for the production of active radicals by H2O2, while instability limits their activation efficiency. In this study, density functional theory calculation (DFT) results showed that Cu+ exhibits excellent H2O2 activation performance, with Gibbs free energy change (ΔG) of 33.66 kcal/mol, two times less than that of Cu2+ (77.83 kcal/mol). Meanwhile, an electro-Fenton system using Cu plate as an anode was proposed for in situ generation of Cu+. The released Cu with low-valence state can be well-confined on the surface of the exciting electrode, which was confirmed by X-ray photoelectron spectroscopy (XPS), Raman, and UV-vis spectroscopy. The hydroxyl radicals in this Cu-based electro-Fenton system were determined by the electron spin resonance (ESR). The nitrobenzene degradation ratio was greatly increased by 43.90% with the introduction of the proposed in situ electrochemical Cu+ generation process. Various characterization results indicated that the production of Cu+ was the key factor in the highly efficient Cu-based electro-Fenton reaction.

Multistep Consolidated Phototherapy Mediated by a NIR-Activated Photosensitizer.

The multifunctional effect of a single molecule for therapeutic functionalities on a single theranostic nanosystem has a great significance to enhance the accuracy of diagnosis and improve the efficacy of therapy. Herein, a biocompatible multistep phototherapeutic system (Ppa-Cy7-PEG-biotin) that contains a photosensitizer pyropheophorbide A (Ppa) with the covalent conjunction of a near-infrared (NIR) cyanine dye (Cy7) was successfully fabricated and functionalized with biotin for flexible specific tumor-targeting phototherapy. These theranostic micelles will disaggregate after NIR irradiation via the photodegradation of cyanine accompanied by the photothermal conversion and the optically controlled release for the restoration of photodynamic function of quenched Ppa. Consecutively, promoted treatments of photosensitive molecules greatly prolonged the tumor retention time and treatment efficiency, having a multistep antitumor effect both in vitro and in vivo. Different from the simple phototherapeutic configurations that only act on the superficial areas of tumors at mild doses, the multistep therapy can be competent for broadly damaging the superficial and deeper regions of tumors at the same dose. Therefore, as opposed to the general combination phototherapeutic approach, this strategy presents a photoactivation-based multistep phototheranostic platform with an enormous potential in enhanced combined phototherapy for cancer.

An oxygen self-sufficient NIR-responsive nanosystem for enhanced PDT and chemotherapy against hypoxic tumors.

The efficacy of photodynamic therapy and chemotherapy is largely limited by oxygen deficiency in the hypoxic tumor microenvironment. To solve these problems, we fabricated a novel NIR-responsive nanosystem which could co-deliver oxygen and anticancer drug DOX. An oxygen self-sufficient amphiphile (F-IR780-PEG) was first synthesized and subsequently utilized to load anticancer drug DOX to form nanoparticles (F/DOX nanoparticles). Due to the high oxygen capacity of such nanoparticles, the hypoxic tumor microenvironment was greatly modulated after these nanoparticles reached the tumor region, and the results revealed that hypoxia-inducible factor α (HIF-1α) was down-regulated and the expression of P-glycoprotein (P-gp) was then reduced, which were in favor of chemotherapy. Under light irradiation at 808 nm, IR780 could efficiently produce singlet oxygen to damage cancer cells by photodynamic therapy (PDT). Simultaneously, the IR780 linkage could be cleaved by singlet oxygen generated by itself and resulted in DOX release, which further caused cell damage by chemotherapy. With the combination of PDT and chemotherapy, F/DOX nanoparticles showed remarkable therapeutic efficacy under in vitro and in vivo conditions. Furthermore, the F/DOX nanoparticles are favorable for imaging-guided tumor therapy due to the inherent fluorescence properties of IR780. We thus believe that the synergistic treatment described here leads to an ideal therapeutic approach to hypoxic tumors.

A Redox Stimulation-Activated Amphiphile for Enhanced Photodynamic Therapy.

The development of more efficient photosensitizers with minimal damage to surrounding normal tissues has been a valuable and challenging subject during photodynamic therapy (PDT). Herein, a stimuli-activated porphyrinic photosensitizer (PEG-TPP-DNB; PEG = poly(ethylene glycol); TPP = 5,10,15,20-tetraphenylporphyrin; DNB = 2,4-dinitrobenzene) with capabilities of fluorescence and, remarkably, singlet oxygen quenching was prepared successfully for photodynamic therapy with high efficiency and biosecurity. The amphiphilic PEG-TPP-DNB could be self-assembled into nanomicelles in aqueous media and dissociated in response to reductive thiol such as glutathione. Meanwhile, the fluorescence and singlet oxygen generation of porphyrinic photosensitizer would be activated to regenerate. Moreover, the intracellular uptake and localization effectively confirmed the redox-responsive and activated behavior of PEG-TPP-DNB micelles. The cytotoxicity in vitro revealed that the micelles had low dark toxicity and great phototoxicity, and in vivo bioimaging and antitumor evaluation further indicated that the micelles possessed selective tumor imaging and targeted PDT antitumor effect as well as low systemic toxicity. Overall, this tumor microenvironment-activated photosensitizer system may provide a useful strategy for precise photodynamic therapy.

Far-Red Light-Induced Reversible Addition-Fragmentation Chain Transfer Polymerization Using a Man-Made Bacteriochlorin.

To overcome the challenge of photoregulated living radical polymerization in long-wavelength radiation, a photoinduced electron transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization in far-red wavelength (λmax = 740 nm) is reported by using a man-made bacteriochlorin as a photocatalyst. A reduced tetraphenylporphyrin (RTPP) having a natural bacteriochlorin macrocycle ring with two reduced pyrrole rings was synthesized with strong absorption in the far-red light region (700-765 nm) and applied for the PET-RAFT polymerization as a photoredox catalyst, which offered excellent control over molecular weight and polydispersities and oxygen tolerance for the polymerization of (methyl) acrylates monomers, and exhibited attractive features of "living" radical polymerization. Benefiting from high penetration of far-red light, the polymerization was also well-controlled when the reaction vessel was covered by translucent animal tissue barriers, for example, skin.

Effective industrial regeneration of arsenic poisoning waste selective catalytic reduction catalyst: contaminants removal and activity recovery.

In this work, an environmental friendly industrial regeneration approach has been proposed to remove the surface poisoning and recover the catalytic activity of waste V2O5-WO3/TiO2 catalyst. Alkaline treatment and acid wash are combined for the waste catalyst regeneration process, which is applied for the arsenic and alkali metal removal, respectively. The crystal structure was well maintained as anatase phase and the surface area was increased during the regeneration, which is favorable for the following active component addition step and regenerated process. The XPS results illustrated that the surface contaminants (arsenic and sodium) were removed and V(IV) was loaded on the regenerated catalyst. Based on the deNOx evaluations, the catalytic activity of the regenerated sample is increased to the level of commercial fresh catalyst. The present industrial regeneration process provides a promising method for the comprehensive recovery of waste catalyst and further understanding in the field of secondary resource recycle.

Hierarchical oxygen-implanted MoS2 nanoparticle decorated graphene for the non-enzymatic electrochemical sensing of hydrogen peroxide in alkaline media.

Owing to the extensive applications of hydrogen peroxide (H2O2) in biological, environmental and chemical engineering, it is of great importance to investigate sensitive and selective sensing platform towards the detection of H2O2. Herein, oxygen-implanted MoS2 nanoparticles decorated graphene nanocomposite is synthesized via a facile one-pot solvothermal method for the sensitive detection of H2O2 in alkaline media. The structure and morphology of the MoS2/graphene nanocomposites were systematically characterized, showing that Mo-O bonds are formed and oxygen is implanted into the crystal structure in the nanocomposite. As a result, the MoS2/graphene composite exhibited enhanced electron transfer kinetics and excellent electro-reduction performance towards H2O2 in alkaline media. Under optimum conditions, the fabricated sensor demonstrated a wide linear response towards H2O2 in the range of 0.25-16mM with a low detection limit of 0.12µM and high sensitivity of 269.7µAmM-1cm-2. Besides, the constructed sensor presented a good selectivity to H2O2 with the presence of other interfering species. Therefore, the proposed sensor was successfully applied for the detection and determination of H2O2 in real sample, indicating great potential for the practical applications.