Heilongjiang University

The design and characterization of metal-organic complexes for optoelectronic applications is an active area of research. The metal-organic complex offers unique optical and electronic properties arising from the interplay between the inorganic metal and the organic ligand. The ability to modify chemical structure through control over metal-ligand interaction on a molecular level could directly impact the properties of the complex. When deposited in thin film form, this class of materials enable the fabrication of a wide variety of low-cost electronic and optoelectronic devices. These include light emitting diodes, solar cells, photodetectors, field-effect transistors as well as chemical and biological sensors. Here we present an overview of recent development in metal-organic complexes with controlled molecular structures and tunable properties. Advances in extending the control of molecular structures to solid materials for energy conversion and information technology applications will be highlighted.

Phosphorus-doped hexagonal tubular carbon nitride (P-TCN) with the layered stacking structure was obtained from a hexagonal rod-like single crystal supramolecular precursor (monoclinic, C2/m). The production process of P-TCN involves two steps: 1) the precursor was prepared by self-assembly of melamine with cyanuric acid from in situ hydrolysis of melamine under phosphorous acid-assisted hydrothermal conditions; 2) the pyrolysis was initiated at the center of precursor under heating, thus giving the hexagonal P-TCN. The tubular structure favors the enhancement of light scattering and active sites. Meanwhile, the introduction of phosphorus leads to a narrow band gap and increased electric conductivity. Thus, the P-TCN exhibited a high hydrogen evolution rate of 67 μmol h(-1) (0.1 g catalyst, λ >420 nm) in the presence of sacrificial agents, and an apparent quantum efficiency of 5.68 % at 420 nm, which is better than most of bulk g-C3 N4 reported.

Mesoporous TiO2 has gained increasing interest because of its outstanding properties and promising applications in a wide range of fields. Herein, we report the facile synthesis of ordered mesoporous black TiO2 (OMBT) materials, which exhibit excellent photocatalytic hydrogen evolution performances. In this case, the employment of a thermally stable and high-surface-area mesoporous TiO2 as the hydrogenation precursor is the key for fabricating the OMBT materials, which not only facilitate H2 gas diffusion into TiO2 and interaction with their structures but also maintain the ordered mesoporous structures as well as inhibit the phase transformation (from anatase to rutile) and crystal growth during hydrogenation at 500 °C. The resultant OMBT materials possess a relatively high surface area of ∼124 m(2) g(-1) and a large pore size and pore volume of ∼9.6 nm and 0.24 cm(3) g(-1), respectively. More importantly, the OMBT materials can extend the photoresponse from ultraviolet to visible and infrared light regions and exhibit a high solar-driven hydrogen production rate (136.2 μmol h(-1)), which is almost two times as high as that of pristine mesoporous TiO2 (76.6 μmol h(-1)).

Chitosan is a product of the deacetylation of chitin, which is widely found in nature. Chitosan is insoluble in water and most organic solvents, which seriously limits both its application scope and applicable fields. However, chitosan contains active functional groups that are liable to chemical reactions; thus, chitosan derivatives can be obtained through the chemical modification of chitosan. The modification of chitosan has been an important aspect of chitosan research, showing a better solubility, pH-sensitive targeting, an increased number of delivery systems, etc. This review summarizes the modification of chitosan by acylation, carboxylation, alkylation, and quaternization in order to improve the water solubility, pH sensitivity, and the targeting of chitosan derivatives. The applications of chitosan derivatives in the antibacterial, sustained slowly release, targeting, and delivery system fields are also described. Chitosan derivatives will have a large impact and show potential in biomedicine for the development of drugs in future.

Polymeric carbon nitride (C3N4) has emerged as the most promising candidate for metal-free photocatalysts but is plagued by low activity due to the poor quantum efficiency and low specific surface area. Exfoliation of bulk crystals into ultrathin nanosheets has proven to be an effective and widely used strategy for enabling high photocatalytic performances; however, this process is complicated, time-consuming, and costly. Here, we report a simple bottom-up method to synthesize porous few-layer C3N4, which involves molecule self-assembly into layered precursors, alcohol molecules intercalation, and subsequent thermal-induced exfoliation and polycondensation. The as-prepared few-layer C3N4 expose more active sites and greatly enhance the separation of charge carriers, thus exhibiting a 26-fold higher hydrogen evolution activity than bulk counterpart. Furthermore, we find that both the high activity and selectivity for the oxidative coupling of amines to imines can be obtained under visible light that surpass those of other metal-free photocatalysts so far.

Sheet-like graphitic carbon with a porous structure can provide low-resistant pathways and short ion-diffusion channels for energy storage, and thus is expected to be an excellent material for high-power supercapacitors. Herein, porous graphene-like nanosheets (PGNSs) with a large surface area were synthesized for the first time via an easy and cost-effective SAG (simultaneous activation–graphitization) route from renewable biomass waste coconut shell. In the synthesis, the graphitic catalyst precursor (FeCl3) and activating agent (ZnCl2) were introduced simultaneously into the skeleton of the coconut shell through coordination of the metal precursor with the functional groups in the coconut shell, thus making simultaneous realization of activation and graphitization of the carbon source under heat treatment. Notably, the iron catalyst in the framework of the coconut shell can generate a carburized phase which plays a key role in the formation of a graphene-like structure during the pyrolytic process. Our results indicated that PGNSs possess good electrical conductivity due to the high graphitic degree, exceptionally high Brunauer–Emmett–Teller surface area (SBET = 1874 m2 g−1) and large pore volume (1.21 cm3 g−1). While being used as a supercapacitor electrode without the use of any conductive additives, PGNSs exhibit a high specific capacitance of 268 F g−1, much higher than that of activated carbon (210 F g−1) fabricated by only activation and graphitic carbon (117 F g−1) by only graphitization at 1 A g−1. Also, PGNSs show superior cycle durability and Coulombic efficiency over 99.5% after 5000 cycles in KOH. Remarkably, in an organic electrolyte, PGNSs also display an outstanding capacitance of 196 F g−1 at 1 A g−1. An energy density of up to 54.7 W h kg−1 could be achieved at a high power density of 10 kW kg−1. The SAG strategy developed here would provide a novel route for low-cost and large-scale production of PGNS electrode materials for high-power supercapacitors.

Nitrogen-doped graphene nanosheets (NGS) with the nitrogen level as high as 10.13 atom% were synthesized via a simple hydrothermal reaction of graphene oxide (GO) and urea. N-doping and reduction of GO were achieved simultaneously under the hydrothermal reaction. In the fabrication, the nitrogen-enriched urea plays a pivotal role in forming the NGS with a high nitrogen level. During the hydrothermal process, the N-dopant of urea could release NH3 in a sustained manner, accompanied by the released NH3 reacting with the oxygen functional groups of the GO and then the nitrogen atoms doped into graphene skeleton, leading to the formation of NGS. The nitrogen level and species could be conveniently controlled by easily tuning the experimental parameters, including the mass ratio between urea and GO and the hydrothermal temperature. Remarkably, in 6 M KOH electrolyte, the synthesized NGS with both high nitrogen (10.13 atom%) and large surface area (593 m2 g−1) exhibits excellent capacitive behaviors (326 F g−1, 0.2 A g−1), superior cycling stability (maintaining initial capacity even) and coulombic efficiency (99.58%) after 2000 cycles. The energy density of 25.02 Wh kg−1 could be achieved at power density of 7980 W kg−1 by a two-electrode symmetric capacitor test. A series of experiments results demonstrated that not only the N-content but also the N-type are very significant for the capacitive behaviors. In more detail, the pyridinic-N and pyrrolic-N play mainly roles for improving pseudo-capacitance by the redox reaction, while quaternary-N could enhance the conductivity of the materials which is favorable to the transport of electrons during the charge/discharge process. Hence, the approach in this work could provide a new way for preparing NGS materials which could be used as advanced electrodes in high performance supercapacitors.

Carbon dots (CDs) are remarkable nanocarriers due to their promising optical and biocompatible capabilities. However, their practical applicability in cancer therapeutics is limited by their insensitive surface properties to complicated tumor microenvironment in vivo. Herein, a tumor extracellular microenvironment-responsive drug nanocarrier based on cisplatin(IV) prodrug-loaded charge-convertible CDs (CDs-Pt(IV)@PEG-(PAH/DMMA)) was developed for imaging-guided drug delivery. An anionic polymer with dimethylmaleic acid (PEG-(PAH/DMMA)) on the fabricated CDs-Pt(IV)@PEG-(PAH/DMMA) could undergo intriguing charge conversion to a cationic polymer in mildly acidic tumor extracellular microenvironment (pH ∼ 6.8), leading to strong electrostatic repulsion and release of positive CDs-Pt(IV). Importantly, positively charged nanocarrier displays high affinity to negatively charged cancer cell membrane, which results in enhanced internalization and effective activation of cisplatin(IV) prodrug in the reductive cytosol. The in vitro experimental results confirmed that this promising charge-convertible nanocarrier possesses better therapeutic efficiency under tumor extracellular microenvironment than normal physiological condition and noncharge-convertible nanocarrier. The in vivo experiments further demonstrated high tumor-inhibition efficacy and low side effects of the charge-convertible CDs, proving its capability as a smart drug nanocarrier with enhanced therapeutic effects. The present work provides a strategy to promote potential clinical application of CDs in the cancer treatment.

Abstract Overall water splitting driven by a low voltage is crucial for practical H 2 evolution, but it is challenging. Herein, anion‐modulation of 3D Ni–V‐based transition metal interstitial compound (TMIC) heterojunctions supported on nickel foam (Ni 3 N‐VN/NF and Ni 2 P‐VP 2 /NF) as coupled hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysts for efficient overall water splitting is demonstrated. The heterointerface in Ni 3 N‐VN has a suitable H* absorption energy, being favorable for enhancing HER activity with onset overpotential (η onset ) of zero and Tafel slope of 37 mV dec −1 in 1 m KOH (close to that of Pt/C/NF). For the OER, the synergy of Ni 2 P‐VP 2 with oxide species can give enhanced activity with η onset of 220 mV and Tafel slope of 49 mV dec −1 . The good activity is ascribed to heterointerface for activating the intermediates, good conductivity of TMICs for electron‐transfer, and porous structure facilitation of mass‐transport. Additionally, the minimal mutual influence of Ni 3 N‐VN/NF and Ni 2 P‐VP 2 /NF allows easy coupling for efficient overall water splitting with a low driving voltage (≥1.43 V), a voltage of 1.51 V at 10 mA cm −2 , and remarkable durability for 100 h. It can be driven by a solar cell (1.5 V), indicating its potential to store intermittent energy.

Due to the increasingly polluted environment and the gradual depletion of fossil fuel reserves, the development of renewable technologies for environmental remediation and energy production is highly desirable. Over the past decades, oxide-based semiconductor photocatalysis has attracted much attention. On various frontiers for efficient photocatalysis, surface-tuning strategies for synthesis and modification of oxides on the nanometer scale have progressed at a fast pace. Hence, it is of significance to review recent advances in the development of surface tuning for oxide-based nanomaterials as activity-enhanced photocatalysts. In this review, special emphases, especially for recent advances in our group, are given to surface tuning of novel nanocrystallites for high thermal stability, hierarchical structure assembly, heterojunctional nanocomposites and high-energy-facet exposure, along with effective testing tools for photogenerated charge properties at the surfaces and/or interfaces. This is of great significance for fields related to energy and environment from scientific and engineering viewpoints.

Abstract Simultaneous highly efficient production of hydrogen and conversion of biomass into value‐added products is meaningful but challenging. Herein, a porous nanospindle composed of carbon‐encapsulated MoO 2 ‐FeP heterojunction (MoO 2 ‐FeP@C) is proposed as a robust bifunctional electrocatalyst for hydrogen evolution reaction (HER) and biomass electrooxidation reaction (BEOR). X‐ray photoelectron spectroscopy analysis and theoretical calculations confirm the electron transfer from MoO 2 to FeP at the interfaces, where electron accumulation on FeP favors the optimization of H 2 O and H* absorption energies for HER, whereas hole accumulation on MoO 2 is responsible for improving the BEOR activity. Thanks to its interfacial electronic structure, MoO 2 ‐FeP@C exhibits excellent HER activity with an overpotential of 103 mV at 10 mA cm −2 and a Tafel slope of 48 mV dec −1 . Meanwhile, when 5‐hydroxymethylfurfural is chosen as the biomass for BEOR, the conversion is almost 100%, and 2,5‐furandicarboxylic acid (FDCA) is obtained with the selectivity of 98.6%. The electrolyzer employing MoO 2 ‐FeP@C for cathodic H 2 and anodic FDCA production requires only a low voltage of 1.486 V at 10 mA cm −2 and can be powered by a solar cell (output voltage: 1.45 V). Additionally, other BEORs coupled with HER catalyzed by MoO 2 ‐FeP@C also have excellent catalytic performance, implying their good versatility.

Abstract Developing non‐precious‐metal bifunctional oxygen reduction and evolution reaction (ORR/OER) catalysts is a major task for promoting the reaction efficiency of Zn–air batteries. Co‐based catalysts have been regarded as promising ORR and OER catalysts owing to the multivalence characteristic of cobalt element. Herein, the synthesis of Co nanoislands rooted on Co–N–C nanosheets supported by carbon felts (Co/Co–N–C) is reported. Co nanosheets rooted on the carbon felt derived from electrodeposition are applied as the self‐template and cobalt source. The synergistic effect of metal Co islands with OER activity and Co–N–C nanosheets with superior ORR performance leads to good bifuctional catalytic performances. Wavelet transform extended X‐ray absorption fine spectroscopy and X‐ray photoelectron spectroscopy certify the formation of Co (mainly Co 0 ) and the Co–N–C (mainly Co 2+ and Co 3+ ) structure. As the air‐cathode, the assembled aqueous Zn–air battery exhibits a small charge–discharge voltage gap (0.82 V@10 mA cm −2 ) and high power density of 132 mW cm −2 , outperforming the commercial Pt/C catalyst. Additionally, the cable flexible rechargeable Zn–air battery exhibits excellent bendable and durability. Density functional theory calculation is combined with operando X‐ray absorption spectroscopy to further elucidate the active sites of oxygen reactions at the Co/Co–N–C cathode in Zn–air battery.

Phosphorus-modified tungsten nitride/reduced graphene oxide (P-WN/rGO) is designed as a high-efficient, low-cost electrocatalyst for the hydrogen evolution reaction (HER). WN (ca. 3 nm in size) on rGO is first synthesized by using the H3[PO4(W3O9)4] cluster as a W source. Followed by phosphorization, the particle size increase slightly to about 4 nm with a P content of 2.52 at %. The interaction of P with rGO and WN results in an obvious increase of work function, being close to Pt metal. The P-WN/rGO exhibits low onset overpotential of 46 mV, Tafel slope of 54 mV dec(-1), and a large exchange current density of 0.35 mA cm(-2) in acid media. It requires overpotential of only 85 mV at current density of 10 mA cm(-2), while remaining good stability in accelerated durability testing. This work shows that the modification with a second anion is powerful way to design new catalysts for HER.

Chitosan is a biodegradable natural polymer with many advantages such as nontoxicity, biocompatibility, and biodegradability. It can be applied in many fields, especially in medicine. As a delivery carrier, it has great potential and cannot be compared with other polymers. Chitosan is extremely difficult to solubilize in water, but it can be solubilized in acidic solution. Its insolubility in water is a major limitation for its use in medical applications. Chitosan derivatives can be obtained by chemical modification using such techniques as acylation, alkylation, sulfation, hydroxylation, quaternization, esterification, graft copolymerization, and etherification. Modified chitosan has chemical properties superior to unmodified chitosan. For example, nanoparticles produced from chitosan derivatives can be used to deliver drugs due to their stability and biocompatibility. This review mainly focuses on the properties of chitosan, chitosan derivatives, and the origin of chitosan-based nanoparticles. In addition, applications of chitosan-based nanoparticles in drug delivery, vaccine delivery, antimicrobial applications, and callus and tissue regeneration are also presented. In summary, nanoparticles based on chitosan have great potential for research and development of new nano vaccines and nano drugs in the future.

Zinc oxide with excellent photocatalytic performance for the photodegradation of dyes (superior to Degussa P25 TiO(2)) could be easily prepared in large quantity by direct calcination of zinc acetate (Zn(Ac)(2)·2H(2)O).

Recently reported colloidal lead halide perovskite quantum dots (QDs) with tunable photoluminescence (PL) wavelengths covering the whole visible spectrum and exceptionally high PL quantum yields (QYs, 50-90%) constitute a new family of functional materials with potential applications in light-harvesting and -emitting devices. By transient absorption spectroscopy, we show that the high PL QYs (∼79%) can be attributed to negligible electron or hole trapping pathways in CsPbBr3 QDs: ∼94% of lowest excitonic states decayed with a single-exponential time constant of 4.5 ± 0.2 ns. Furthermore, excitons in CsPbBr3 QDs can be efficiently dissociated in the presence of electron or hole acceptors. The half-lives of electron transfer (ET) to benzoquinone and subsequent charge recombination are 65 ± 5 ps and 2.6 ± 0.4 ns, respectively. The half-lives for hole transfer (HT) to phenothiazine and the subsequent charge recombination are 49 ± 6 ps and 1.0 ± 0.2 ns, respectively. The lack of electron and hole traps and fast interfacial ET and HT rates are key properties that may enable the development of efficient lead halide perovskite QDs-based light-harvesting and -emitting devices.

Abstract An in situ catalytic etching strategy is developed to fabricate holey reduced graphene oxide along with simultaneous coupling with a small‐sized Mo 2 N–Mo 2 C heterojunction (Mo 2 N–Mo 2 C/HGr). The method includes the first immobilization of H 3 PMo 12 O 40 (PMo 12 ) clusters on graphite oxide (GO), followed by calcination in air and NH 3 to form Mo 2 N–Mo 2 C/HGr. PMo 12 not only acts as the Mo heterojunction source, but also provides the Mo species that can in situ catalyze the decomposition of adjacent reduced GO to form HGr, while the released gas (CO) and introduced NH 3 simultaneously react with the Mo species to form an Mo 2 N–Mo 2 C heterojunction on HGr. The hybrid exhibits superior activity towards the hydrogen evolution reaction with low onset potentials of 11 mV (0.5 m H 2 SO 4 ) and 18 mV (1 m KOH) as well as remarkable stability. The activity in alkaline media is also superior to Pt/C at large current densities (>88 mA cm −2 ). The good activity of Mo 2 N–Mo 2 C/HGr is ascribed to its small size, the heterojunction of Mo 2 N–Mo 2 C, and the good charge/mass‐transfer ability of HGr, as supported by a series of experiments and theoretical calculations.

Ag-TiO2 catalysts with different Ag contents were prepared via a sol-gel method in the absence of light. Based on the characterizations of XRD, photoluminescence (PL), surface photovoltage spectroscopy (SPS), field-induced surface photovoltage spectroscopy (FISPS), and XPS as well as the evaluation of the photocatalytic activity for degrading rhodamine B(RhB) solutions, it was found that the Ag dopant promoted the phase transformation as well as had an inhibition effect on the growth of anatase crystallite. The PL and SPS intensities were decreased with increasing Ag content, indicating that the Ag dopant could effectively inhibit the recombination of the photoinduced electrons and holes. However, the active sites capturing the photoinduced electrons reduced, while the Ag content exceeded 5 mol %. At rather low Ag dopant concentrations, the migration and diffusion of Ag+ ions were predominant, while at rather high Ag dopant concentrations, the migration, diffusion, and reduction of Ag ions simultaneously occurred. The Ag-TiO2 photocatalysts with appropriate content of Ag (Ag species concentration is from about 3 to 5 mol %) possessed abundant electron traps so as to be favorable for the separation of the photoinduced electron-hole pairs, which could greatly enhance the activity of the photocatalysts. From the results of FISPS measurements, it could be found that the impurity bands and abundant surface states were introduced into the interfacial layer of TiO2 because of Ag simultaneously doping and depositing, which could improve the absorption capability for visible light of the photocatalysts.

Abstract Dual‐metal single‐atom catalysts exhibit superior performance for oxygen reduction reaction (ORR), however, the synergistic catalytic mechanism is not deeply understood. Herein, we report a dual‐metal single‐atom catalyst consisted of Cu−N 4 and Zn−N 4 on the N‐doped carbon support (Cu/Zn−NC). It exhibits high‐efficiency ORR activity with an E onset of 0.98 V and an E 1/2 of 0.83 V, excellent stability (no degradation after 10 000 cycles), surpassing state‐of‐the‐art Pt/C and great mass of Pt‐free single atom catalysts. Operando XANES demonstrates that the Cu−N 4 as active center experiences the change from atomic dispersion to cluster with the cooperation of Zn−N 4 during ORR process, and then turns to single atom state again after reaction. DFT calculation further indicates that the adjustment effect of Zn on the d‐orbital electron distribution of Cu could benefit to the stretch and cleavage of O‐O on Cu active center, speeding up the process of rate determining step of OOH*.

This review highlights breakthroughs in the past decade in the synthesis and the modification of both the chemistry and morphology of Li₄Ti₅O₁₂.