Preparation of a novel injectable in situ-gelling nanoparticle with applications in controlled protein release and cancer cell entrapment

Temperature sensitive injectable hydrogels have been used as drug/protein carriers for a variety of pharmaceutical applications. Oligo(ethylene glycol) methacrylate (OEGMA) monomers with varying ethylene oxide chain lengths have been used for the synthesis of in situ forming hydrogel. In this study, a new series of thermally induced gelling hydrogel nanoparticles (PMOA hydrogel nanoparticles) was developed by copolymerization with di(ethylene glycol) methyl ether methacrylate (MEO₂MA), poly(ethylene glycol) methyl ether methacrylate (300 g mol⁻¹, OEGMA₃₀₀), and acrylic acid (AAc). The effects of acrylic acid content on the physical, chemical, and biological properties of the nanoparticle-based hydrogels were investigated. Due to its high electrostatic properties, addition of AAc increases LCST as well as gelation temperature. Further, using Cy5-labelled bovine serum albumin and erythropoietin (Epo) as model drugs, studies have shown that the thermogelling hydrogels have the ability to tune the release rate of these proteins in vitro. Finally, the ability of Epo releasing hydrogels to recruit prostate cancer cells was assessed in vivo. Overall, our results support that this new series of thermally induced gelling systems can be used as protein control releasing vehicles and cancer cell traps.

At body temperature, thermosensitive nanoparticles release erythropoietin to lure metastatic cancer cells.     

Bilayer graphene/HgCdTe based very long infrared photodetector with superior external quantum efficiency,responsivity, and detectivity

We present a high-performance bilayer graphene (BLG) and mercury cadmium telluride (Hg_1−xCd_x=0.1867Te) heterojunction based very long wavelength infrared (VLWIR) conductive photodetector. The unique absorption properties of graphene enable a long carrier lifetime of charge carriers contributing to the carrier-multiplication due to impact ionization and, hence, large photocurrent and high quantum efficiency. The proposed p⁺-BLG/n-Hg_0.8133Cd_0.1867Te photodetector is characterized and analyzed in terms of different electrical and optical characteristic parameters using computer simulations. The obtained results are further validated by developing an analytical model based on drift-diffusion, tunneling and Chu''s methods. The photodetector has demonstrated a superior performance including improved dark current density (∼1.75 × 10⁻¹⁴ µA cm⁻²), photocurrent density (∼8.33 µA cm⁻²), internal quantum efficiency (QE_int ∼ 99.49%), external quantum efficiency (QE_ext ∼ 89%), internal photocurrent responsivity (∼13.26 A W⁻¹), external photocurrent responsivity (∼9.1 A W⁻¹), noise equivalent power (∼8.3 × 10⁻¹⁸ W), total noise current (∼1.06 fA), signal to noise ratio (∼156.18 dB), 3 dB cut-off frequency (∼36.16 GHz), and response time of 9.4 ps at 77 K. Furthermore, the effects of different external biasing, light power intensity, and temperature are evaluated, suggesting a high QE_ext of 3337.70% with a bias of −0.5 V near room temperature.

We present a high-performance bilayer graphene (BLG) and mercury cadmium telluride (Hg_1−xCd_x=0.1867Te) heterojunction based very long wavelength infrared (VLWIR) conductive photodetector.     

Preparation of glycoside polymer micelles with antioxidant polyphenolic cores using alkylated poly(arbutin)s

This paper describes the synthesis of long-chain-alkylated poly(arbutin)s (poly(Arb)-R_x, where R = alkyl-chain length and x = degree of substitution (DS)) and their aqueous micelle formation. DS was controlled by tailoring the alkyl reagent/main-chain phenol substituent feed ratio. The critical micelle concentrations (CMCs) of poly(Arb)-R_x were determined as 1.3–5.2 mg mL⁻¹ by the surface tension method. Introduction of longer alkyl substituents decreased CMC and also decreased aqueous solubility. In DLS measurement, the average micelle diameters were 225–616 nm, and micelle size decreased with increasing DS because of increased stabilization by hydrophobic alkyl substituents. Transmission electron microscopy indicated that mainly wormlike cylindrical micelles were formed, even with highly hydrophilic polymers. The alkylated polymer exhibited no cytotoxicity, and their antioxidant abilities were evaluated by the β-carotene bleaching method. Only 0.049 mol equivalents of poly(Arb)-C8₃₀ to linoleic acid was sufficient to preserve the β-carotene.

This paper describes the synthesis of long-chain-alkylated poly(arbutin)s (poly(Arb)-R_x, where R = alkyl-chain length and x = degree of substitution (DS)) and their aqueous micelle formation.     

Correlation of crystal structure and optical properties of Ba0.97Nd0.0267Ti(1-x)WxO3 perovskite

The Ba_0.97Nd_0.0267Ti_(1−x)W_xO₃ (BNT_x) pervoskite with a single phase tetragonal structure was prepared at 900 °C using the Molten salt method. Raman spectra, Fourier transform infrared spectra (FT-IR), absorption spectra (Vis-NIR) and photoluminescence spectra (PL) in the temperature range from 10–300 K were used to investigate the correlations between the crystal structure and the optical properties of BNT_x ceramics. Raman analyses and FT-IR indicated that the W⁶⁺ ions are incorporated sufficiently into into the BNT_x lattice. The optical absorption spectra were recorded in the wavelength range of 400–1000 nm. The optical band gap (E_g) and Urbach energy (E_u) values were calculated from the absorption spectra. The emission spectra exhibited three prominent peaks located at 880, 1058 and 1340 nm corresponding to the ⁴F_3/2 → ⁴I_{9/2,11/2,13/2} transition levels, respectively. They also showed a decrease in the intensity of emission spectra following the addition of W⁶⁺ ions. This decrease is due to the slight changes in the crystal environment around Nd³⁺ and the non-radiative energy transfer. According to the PL measurements, the study of power-excitation density confirmed that two photons at low energy are required to create the down-conversion (DC) emissions, implying that they may also have important applications as DC materials.

The Ba_0.97Nd_0.0267Ti_(1−x)W_xO₃ (BNT_x) pervoskite with a single phase tetragonal structure was prepared at 900 °C using the Molten salt method.     

Covalent incorporation of tobacco mosaic virus increases the stiffness of poly(ethylene glycol) diacrylate hydrogels

Hydrogels are versatile materials, finding applications as adsorbers, supports for biosensors and biocatalysts or as scaffolds for tissue engineering. A frequently used building block for chemically cross-linked hydrogels is poly(ethylene glycol) diacrylate (PEG-DA). However, after curing, PEG-DA hydrogels cannot be functionalized easily. In this contribution, the stiff, rod-like tobacco mosaic virus (TMV) is investigated as a functional additive to PEG-DA hydrogels. TMV consists of more than 2000 identical coat proteins and can therefore present more than 2000 functional sites per TMV available for coupling, and thus has been used as a template or building block for nano-scaled hybrid materials for many years. Here, PEG-DA (M_n = 700 g mol⁻¹) hydrogels are combined with a thiol-group presenting TMV mutant (TMV_Cys). By covalent coupling of TMV_Cys into the hydrogel matrix via the thiol-Michael reaction, the storage modulus of the hydrogels is increased compared to pure PEG-DA hydrogels and to hydrogels containing wildtype TMV (wt-TMV) which is not coupled covalently into the hydrogel matrix. In contrast, the swelling behaviour of the hydrogels is not altered by TMV_Cys or wt-TMV. Transmission electron microscopy reveals that the TMV particles are well dispersed in the hydrogels without any large aggregates. These findings give rise to the conclusion that well-defined hydrogels were obtained which offer the possibility to use the incorporated TMV as multivalent carrier templates e.g. for enzymes in future studies.

Tuning hydrogel properties with viruses.     

Triple network hydrogels (TN gels) prepared by a one-pot,two-step method with high mechanical properties

In this work, poly(vinyl alcohol) (PVA) was incorporated into the networks of polyacrylamide/polyacrylic acid (PAM/PAA) to prepare novel PAM/PAA/PVA Triple-network (TN) hydrogels by an in situ polymerization and repeated freezing–thawing (F–T) process. The TN hydrogels have not only high mechanical strength, but also a moderate swelling ability by varying the weight ratio of calcium chloride (CaCl₂) and PVA and free shaping. The compressive stress of the as-prepared hydrogels could reach 11 MPa, and the highest stretching stress could reach 0.8 MPa. Upon mechanical loading, the coordination network between PAA and CaCl₂ served as sacrificial bonds to efficiently dissipate energy. However, they can reform when the mechanical load is released, resulting from the fast coordination between PAA and Ca²⁺. Therefore, TN hydrogels have potential application in biomaterials.

TN hydrogels with high mechanical properties are prepared and they have potential application in biomaterials.     

Expanded graphite/NiAl layered double hydroxide nanowires for ultra-sensitive,ultra-low detection limits and selective NOx gas detection at room temperature

To develop an ultra-sensitive and selective NO_x gas sensor with an ultra-low detection limit, expanded graphite/NiAl layered double hydroxide (EG/NA) nanowires were synthesized by using hydrothermal method with EG as a template and adjusting the amount of urea in the reaction. X-ray diffraction and transmission electron microscopy showed EG/NA3 nanowires with a diameter of 5–10 nm and a length greater than 100 nm uniformly dispersed on the expanded graphite nanosheet (>8 layers). The synergy between NiAl layered double hydroxide (NiAl-LDH) and expanded graphite (EG) improved the gas sensing properties of the composites. As expected, gas sensing tests showed that EG/NA composites have superior performance over pristine NiAl-LDH. In particular, the EG/NA3 nanowire material exhibited an ultra-high response (R_a/R_g = 17.65) with ultra-fast response time (about 2 s) to 100 ppm NO_x, an ultra-low detection limit (10 ppb) and good selectivity at room temperature (RT, 24 ± 2 °C), which could meet a variety of application needs. Furthermore, the enhancement of the sensing response was attributed to the nanowire structure formed by NiAl-LDH in the EG interlayer and the conductive nanonetwork of interwoven nanowires.

Expanded graphite/NiAl-LDH nanowires for ultra-sensitive, ultra-low detection limits and selective NO_x gas detection at room temperature.     

Composition design,electrical properties,and temperature stability in (1 − x)K0.44Na0.56Nb0.96Sb0.04O3-xBi0.45La0.05Na0.5ZrO3 lead-free ceramics

In this work, we designed a new system of (1 − x)K_0.44Na_0.56Nb_0.96Sb_0.04O₃-xBi_0.45La_0.05Na_0.5ZrO₃ (KNNS-xBLNZ, 0 ≤ x ≤ 0.06) ceramics, and systemically investigated both their electrical performance and temperature stability. Through optimizing the composition, a relatively good comprehensive performance (e.g., d₃₃ ∼ 455 ± 10 pC N⁻¹, k_p ∼ 0.47 ± 0.02, T_C ∼ 266 °C, strain ∼ 0.148%, and ) is obtained in the ceramics with x = 0.040, which is attributed to the construction of a rhombohedral–orthorhombic–tetragonal (R–O–T) phase boundary. Moreover, a good temperature stability of remnant polarization (P_r) as well as strain value (P_{r100 °C}/P_rRT ∼ 89.6%, P_{r180 °C}/P_rRT ∼ 73.2%, S_{100 °C}/S_RT ∼ 92.6%, S_{180 °C}/S_RT ∼ 74.1%) is gained in KNNS-0.040BLNZ ceramics with a broad temperature range from room temperature to 180 °C. Hence, we believe that KNNS-xBLNZ ceramics opens a window for the practical application of lead-free ceramics.

A new system of (1 – x)K_0.44Na_0.56Nb_0.96Sb_0.04O₃-xBi_0.45La_0.05Na_0.5ZrO₃ (KNNS-xBLNZ, 0 ≤ x ≤ 0.06) ceramics was designed, and systemically investigated both their electrical performance and temperature stability.     

First-principles study of the adsorption behaviors of Li atoms and LiF on the CFx (x = 1.0, 0.9, 0.8, 0.5, ∼0.0) surface

Based on first principles calculation, the adsorption properties of Li atoms and LiF molecules on the fluorographene (CF_x) surface with different F/C ratios (x = 1.0, 0.9, 0.8, 0.5 and ∼0.0) have been studied in the present work. The calculated binding energy of Li and CF_x is greater than 2.29 eV under different F/C ratios, indicating that the battery has the potential to maintain a high discharge platform during the whole discharge process. But the adsorption energies of LiF on a CF_x layer for different F/C ratios are 0.12–1.04 eV, which means LiF is not easy to desorb from a CF_x surface even at room temperature. It will stay on the surface for a long time and affect the subsequent discharge. Current calculations also show the structure of the CF_x-skeleton will change greatly during the reaction, when there are many unsaturated carbon atoms on the CF_x surface, such as at x = 0.8 and 0.5. Moreover, the discharge voltage is strongly dependent on the discharge site. After discharge, the CF_x-skeleton may continue to relax and release a lot of heat energy.

Based on first principles calculation, the adsorption properties of Li atoms and LiF molecules on the fluorographene (CF_x) surface with different F/C ratio (x = 1.0, 0.9, 0.8, 0.5 and ∼0.0) have been studied in the present work.     

Effects of polymers on the properties of hydrogels constructed using sodium deoxycholate and amino acid

The gelation behavior and properties of sodium deoxycholate (NaDC) and l-aspartic acid (Asp) in aqueous solution were investigated in detail at 25 °C. The linear polymer poly(2-(2-methoxyethoxy)ethyl methacrylate-co-oligo-(ethylene glycol) methacrylate) (P(MEO₂MA₉₀-co-OEGMA₁₀)) and star-shaped polymer poly(2-(dimethylamino)ethyl methacrylate-b-2-(2-methoxyethoxy)ethyl methacrylate) (CDPDPM) were introduced in NaDC/Asp hydrogels for exploring the effects of polymers on the properties of NaDC/Asp hydrogels and the mechanism underlying gelation processes by polymers was proposed. The hydrogels were characterized by phase behavior observation, polarized optical microscopy (POM), cryogenic scanning electron microscopy (cryo-SEM), X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and rheological measurements. Moreover, the adsorption performances of hydrogels with and without polymers to methylene blue (MB) were studied using a UV-vis spectrometer. The results indicated that the transition from sol to gel state was observed with an increase in the Asp concentration in the system. Both linear and star-shaped polymers can participate in the formation of a gel network structure, so that the density of network structure and the mechanical strength of hydrogels increased. Furthermore, it was found that the viscoelasticity of the CDPDPM-containing hydrogel was much higher than that of the P(MEO₂MA₉₀-co-OEGMA₁₀)-containing hydrogel under the same condition, indicating that CDPDPM performed better in strengthening the network structure of the hydrogels than P(MEO₂MA₉₀-co-OEGMA₁₀) due to the special structure that provided more binding sites for hydrogen bonding and stronger hydrophobicity that inhibited the swelling and dissolution of hydrogels. On coming in contact with the MB solution, the CDPDPM-containing hydrogel can adsorb MB and maintain the hydrogel state for recycling. On the contrary, the NaDC/Asp hydrogel dissolved and P(MEO₂MA₉₀-co-OEGMA₁₀)-containing hydrogel collapsed in the MB solution. The properties of the hydrogels are expected to be tailored by introducing polymers with different properties, including the charge numbers, the number of available binding sites, and hydrophobic properties.

Polymer can participate in the formation of hydrogel network structure and provide a lot of binding sites, leading to an enhancement of the mechanical strength of the hydrogels.     

Significant enhancement of dielectric permittivity and percolation behaviour of La2−xSrxNiO4/poly(vinylidene fluoride) composites with different Sr doping concentrations

The percolation behaviour and dielectric properties of La_2−xSr_xNiO₄ (LSNO)/poly(vinylidene fluoride) (PVDF) composites with different Sr doping concentrations were investigated. The semiconducting LSNO filler particles with x = 0.2 (LSNO-1) and x = 0.4 (LSNO-2) were prepared using a chemical combustion method. The microstructures, thermal properties, and phase compositions of the polymer composites and filler particles were systematically investigated. The conductivity of the LSNO fillers increased with the Sr content and had an important impact on the dielectric properties of the LSNO/PVDF composites. The percolation threshold of the LSNO-2/PVDF composite was lower than that of the LSNO-1/PVDF composite. An ultra-high dielectric permittivity (ε′) of 3384.7 (at 1 kHz and room temperature), which was approximately 340 times higher than that of pure PVDF, was obtained for the LSNO-2/PVDF composite with a filler volume fraction of 25 vol%. The enhanced dielectric properties were attributed to interfacial polarisation at the semiconductor–insulator interface, a micro-capacitor model, and the intrinsically remarkable dielectric properties of the LSNO ceramic.

The percolation behaviour and dielectric properties of La_2−xSr_xNiO₄ (LSNO)/poly(vinylidene fluoride) (PVDF) composites with different Sr doping concentrations were investigated.     

Triazole-based cross-linkers in radical polymerization processes: tuning mechanical properties of poly(acrylamide) and poly(N,N-dimethylacrylamide) hydrogels

Triazole-based cross-linkers with different spacer lengths and different functional end groups (acrylamides, methacrylamides, maleimides and vinylsulfonamides) were synthesized, investigated for cytotoxic and antibacterial activity, and incorporated into poly(acrylamide) (PAAm) and poly(N,N-dimethylacrylamide) (PDMAAm) hydrogels by free-radical polymerization. Hydrogels prepared with different cross-linkers and cross-linker contents between 0.2% and 1.0% were compared by gel yields, equilibrium degrees of swelling (S) and storage moduli (G′). Generally with increasing cross-linker content, G′ values of the hydrogels increased, while S values decreased. The different polymerizable cross-linker end groups resulted in a decrease of G′ in the following order for cross-linkers with C₄ spacers: acrylamide > maleimide > methacrylamide > vinylsulfonamide. Longer cross-linker alkyl spacer lengths caused an increase in G′ and a decrease in S. Independent of the cross-linker used, a universal correlation between G′ and equilibrium polymer volume fraction ϕ was found. For PAAm hydrogels, G′ ranged between 4 kPa and 23 kPa and ϕ between 0.07 and 0.14. For PDMAAm hydrogels, G′ ranged between 0.1 kPa and 4.9 kPa and ϕ between 0.02 and 0.06. The collected data were used to establish an empirical model to predict G′ depending on ϕ. G′ of PAAm and PDMAAm hydrogels is given by G′ = 4034 kPa ϕ^2.66 and G′ = 4297 kPa ϕ^2.46, respectively.

Poly(acrylamide) and poly(N,N-dimethylacrylamide) hydrogels were prepared by free-radical polymerization using triazole-based cross-linkers with different spacer lengths and functional end groups and hydrogel properties were assessed.     

Improving the intrinsic thermal stability of the MAPbI3 perovskite by incorporating cesium 5-aminovaleric acetate

Cesium 5-aminovaleric acetate (NH₂C₄H₈COOCs) was used to improve the intrinsic thermal stability of the methylammonium lead triiodide (MAPbI₃) perovskite. The corresponding carbon-based perovskite solar cells without encapsulation showed favourable stability at 100 °C for 500 h.

Cesium 5-aminovaleric acetate (NH₂C₄H₈COOCs) was used to improve the intrinsic thermal stability of the methylammonium lead triiodide (MAPbI₃) perovskite.

Next-generation solar cells have the prerequisite of low-cost and easy to fabricate are the prerequisites of next-generation printable solar cells. In recent years, printable solar cells based on ABX₃ (where A is typically methylammonium (MA), formamidinium (FA), or Cs; B is Pb or Sn; and X is I, Br or Cl) perovskite-type light absorbers have attracted widespread attention for their high power conversion efficiencies (PCEs) combining with low processing costs. At present, the record PCE for any perovskite solar cell (PSC) is 22.7%,¹ which is on a par with those of mainstream multi-crystalline silicon solar devices. Obviously, the high PCE together with easy fabrication procedures make PSCs a captivating device for future applications.Typically PSCs need a vacuum system to evaporate a noble metal (Ag or Au) as the back contact. However, the use of vacuum system and expensive metal targets with high purity doesn''t suit the purpose of low-cost printing. In this regard, the carbon-based perovskite solar cells,² which substitute the noble metal electrode with a printable carbon electrode, have enormous potential for realizing the application of fully printed, low-cost photovoltaics. To date, many groups from all over the world have put much energy into the study of improving the performance of such PSCs with mesoporous carbon electrodes. Strategies including surface modification,^3–5 materials engineering,^6–11 solvent engineering^12–14 and post-treatments^15–17 have been applied in carbon-based PSCs for pursuing higher efficiencies. As a result, the reported PCE of carbon-based PSCs has increased rapidly from 6.6%² to 17%¹⁸ in just a few years. And, at the same time, carbon-based PSCs have been reported that can be easily printed into large-scale modules.¹⁹ However, just like any other kind of PSC, long-term stability is still a problem for the final commercialization of this emerging photovoltaic technology.²⁰ Solar modules are exposed to elevated temperatures during operation; hence as per the international standard (IEC 61646 climatic chamber tests), a solar panel must show thermal stability up to 85 °C.²¹ The formation energy for the MAPbI₃ perovskite is 0.11–0.14 eV, which is close to 0.093 eV, suggesting possible degradation at a continuous exposure to a temperature of 85 °C. Recently, formamidinium cation (FA⁺)- and Cs⁺- based perovskites have demonstrated better thermal stability levels than has pure MAPbI₃. However, FAPbI₃ and CsPbI₃ perovskites are more sensitive to humidity, which requires higher costs for encapsulation.^22,23In carbon-based PSCs, perovskite crystals are loaded in the mesopores, and their grain sizes are restricted by the pore size. In comparison to the perovskite crystals with large grains in traditional PSCs, perovskite crystals with small grains in carbon-based PSCs show much poorer heat tolerance. For this reason, all of the carbon-based PSCs using an MAPbI₃ perovskite light absorber can only be annealed at 50–70 °C.^2,4,8,16,19 From this perspective, enhancing the intrinsic heat tolerance of perovskite materials would be of great significance for the development of carbon-based PSCs.Herein, we used cesium 5-aminovaleric acetate (NH₂C₄H₈COOCs) as an additive of MAPbI₃ perovskite, and found that Cs_xMA_1−xPb(5-AVA)_xI_3−x perovskite showed high heat tolerance, even at 150 °C. Based on previous work,⁸ 5-ammonium valeric acid (5-AVA) hydriodide (NH₂C₄H₈COOH·HI), which was obtained from acid (HI) hydrolysis of 5-AVA, could create mixed-cation perovskite (5-AVA)_x(MA)_1−xPbI₃ crystals with preferable stability in ambient air under full sunlight. Since 5-AVA is an amphipathic molecule, we employed CsOH to synthesize the alkaline hydrolysis product of 5-AVA (see ESI^† for the synthesis details), aiming at combining the positive effects of the 5-AVA group and Cs⁺ cation in the MAPbI₃ perovskite.The molecular structures of (5-AVA) iodide and Cs-(5-AVA) acetate are shown in Fig. 1a. Via replacing 5% (in molar ratio) of MAI in the MAPbI₃ perovskite with (5-AVA) iodide and Cs-(5-AVA) acetate, we obtained the (5-AVA)_x(MA)_1−xPbI₃ perovskite and Cs_xMA_1−xPb(5-AVA)_xI_3−x perovskite, respectively. Note that 5-AVA served as a cation in the (5-AVA)_x(MA)_1−xPbI₃ perovskite, while in the Cs_xMA_1−xPb(5-AVA)_xI_3−x perovskite, 5-AVA took the place of the I⁻ anion. This little difference resulted in different solubilities of the (5-AVA)_x(MA)_1−xPbI₃ perovskite and Cs_xMA_1−xPb(5-AVA)_xI_3−x perovskite in γ-butyrolactone (GBL) solvent. As shown in Fig. 1b, the turbid (5-AVA)_x(MA)_1−xPbI₃ perovskite solution (1 M in GBL) showed a lot of yellowish precipitate at room temperature. However, the Cs_xMA_1−xPb(5-AVA)_xI_3−x perovskite solution was much clearer, indicating the Cs_xMA_1−xPb(5-AVA)_xI_3−x perovskite to be more soluble than the (5-AVA)_x(MA)_1−xPbI₃ perovskite. We attributed the good solubility of Cs_xMA_1−xPb(5-AVA)_xI_3−x perovskite in GBL to the exposed amino group of the Cs-(5-AVA) acetate.Open in a separate windowFig. 1(a) The molecular structure of (5-AVA) iodide and Cs-(5-AVA) acetate. (b) Optical images of (5-AVA)_x(MA)_1−xPbI₃ and Cs_xMA_1−xPb(5-AVA)_xI_3−x perovskite solution at room temperature.X-ray diffraction (XRD) measurements were taken to identify the crystal structure of the as prepared perovskites. On glass substrate, both of the Cs_xMA_1−xPb(5-AVA)_xI_3−x and (5-AVA)_x(MA)_1−xPbI₃ perovskite patterns showed similar diffraction peaks at 14.18°, 23.5°, 24.5° 28.56° and 31.05°, indicating the same tetragonal MAPbI₃ perovskite crystal structure.²⁴ What''s more, the intensities of the Cs_xMA_1−xPb(5-AVA)_xI_3−x peaks were much stronger than those of the (5-AVA)_x(MA)_1−xPbI₃ perovskite peaks. Since the two kinds of perovskite samples were fabricated and measured using the same conditions, we concluded the Cs-(5-AVA) acetate to be beneficial for the growth of the MAPbI₃ perovskite (Fig. 2).Open in a separate windowFig. 2XRD patterns of the PbI₂, (5-AVA)_x(MA)_1−xPbI₃ and Cs_xMA_1−xPb(5-AVA)_xI_3−x films on glass substrates.By using these two kinds of perovskite materials, we fabricated carbon-based PSCs according to the method reported previously.² Briefly, by using the screen printing technique, mesoporous TiO₂, ZrO₂ and carbon films were successively deposited on the FTO substrates, which had been coated with compact TiO₂ beforehand. And then, a perovskite light absorber was loaded by filling the precursor solution into the mesoporous carbon/ZrO₂/TiO₂ layers (see Fig. 3a). The microstructure of a cross-section of the as-prepared device was observed using SEM, and each layer showed well-defined boundaries and a uniform thickness (see Fig. 3b), and the distribution of the perovskite in the mesoporous films was homogenous (EDS images are shown in Fig. S1^†). After the filling procedure, the devices were dried on a hot plate, and after the removal of GBL solvent, we finally obtained the carbon-based PSCs. For the sake of comparison, the drying temperature was set at 100 °C, which was much higher than the conventionally used temperature⁸ (50 °C).Open in a separate windowFig. 3(a) Schematic structure of the carbon-based PSC. (b) SEM image from a cross-section of the carbon-based PSC.Two groups of the carbon-based PSCs (with each group consisting of eight devices) were fabricated by using the Cs_xMA_1−xPb(5-AVA)_xI_3−x and (5-AVA)_x(MA)_1−xPbI₃ perovskites, respectively. Under standard AM1.5 illumination (100 mW cm⁻²), the devices using the Cs_xMA_1−xPb(5-AVA)_xI_3−x perovskite generally showed a higher PCE than did the (5-AVA)_x(MA)_1−xPbI₃ perovskite. (Details of the photovoltaic parameters are summarized in Table S1.^†) J–V curves of the corresponding best devices are shown in Fig. 4a. With the Cs_xMA_1−xPb(5-AVA)_xI_3−x perovskite, the best device showed a photocurrent density (J_sc) of 20.59 mAcm⁻² (with J_sc determined from the IPCE spectra in Fig. S2^†), an open circuit voltage (V_oc) of 893 mV, a fill factor (FF) of 0.66 and an overall PCE of 12.19%. In contrast, the best device using the (5-AVA)_x(MA)_1−xPbI₃ perovskite showed a much lower PCE of 9.50% (J_sc = 16.78 mAcm⁻², V_oc = 830 mV and FF = 0.68). Moreover, the long-term stability levels of the best devices without encapsulation were determined at 100 °C in a glove box (see Fig. 4b). After 500 h, the PCE of the (5-AVA)_x(MA)_1−xPbI₃-based device decayed gradually from 9.50% to 4.1%, i.e., a reduction of 56.8%. Surprisingly, the Cs_xMA_1−xPb(5-AVA)_xI_3−x-based device maintained 88% (decay from 12.19% to 10.73%) of its initial PCE after 500 h, indicating favourable thermal stability at 100 °C.Open in a separate windowFig. 4(a) J–V curves of the carbon-based PSCs with the (5-AVA)_x(MA)_1−xPbI₃ and Cs_xMA_1−xPb(5-AVA)_xI_3−x perovskites. (b) Long-term stability of the carbon-based PSCs stored at 100 °C in glove box.Further XRD measurements were taken to confirm the difference between the thermal stability of the (5-AVA)_x(MA)_1−xPbI₃ perovskite and that of the Cs_xMA_1−xPb(5-AVA)_xI_3−x perovskite. The (5-AVA)_x(MA)_1−xPbI₃ perovskite, after having been heated on a hot plate at 75 °C for 24 h, yielded an XRD pattern showing a small peak at 2θ = 12.63°, indicating that part of the perovskite was decomposed into PbI₂. As the temperature was increased, the intensity of the PbI₂ diffraction peak became increasingly stronger, and the colour of (5-AVA)_x(MA)_1−xPbI₃ perovskite film on glass gradually changed from black to yellow (see Fig. 5a). However, compared with the (5-AVA)_x(MA)_1−xPbI₃ perovskite, the Cs_xMA_1−xPb(5-AVA)_xI_3−x perovskite displayed a much lower thermal decomposition rate. As shown in Fig. 5b, even after having been heated at 150 °C for 24 h, most of the Cs_xMA_1−xPb(5-AVA)_xI_3−x perovskite still kept the perovskite phase (see Fig. 5b).Open in a separate windowFig. 5XRD patterns and optical images (inset) of (a) (5-AVA)_x(MA)_1−xPbI₃ and (b) Cs_xMA_1−xPb(5-AVA)_xI_3−x perovskite films exposed on a hot plate to various temperatures each for 24 h.To further identify any possible effects of the (5-AVA) anion and Cs cation on the thermal stability of the MAPbI₃ perovskite, we also compared the decomposition process of MAPb(5-AVA)_xI_3−x with that of Cs_xMA_1−xPbI_3−x (see Fig. S3^†). The XRD results showed that including 5% Cs⁺ individually or 5% (5-AVA)⁻ individually in the MAPbI₃ perovskite sample did not much enchance the thermal stability of the sample. Hence, we attributed the good thermal stability of the Cs_xMA_1−xPb(5-AVA)_xI_3−x perovskite to the unique Cs-(5-AVA) acetate additive. Since the 5-AVA group can act as a templating agent in perovskites^8,25,26 and the Cs⁺ cation has a strong bonding energy with the I⁻ anion, the migration of ions in the Cs_xMA_1−xPb(5-AVA)_xI_3−x perovskite could be suppressed by the 2D/3D interfaces²⁷ and the high migration activation energy of the inorganic cation.²⁸     

Unexpected visible light driven photocatalytic activity without cocatalysts and sacrificial reagents from a (GaN)1–x(ZnO)x solid solution synthesized at high pressure over the entire composition range

Optical and photocatalytic properties were determined for the solid solution series (GaN)_1–x(ZnO)_x synthesized at high pressure over the entire compositional range (x = 0.07 to 0.9). We report for the first time photocatalytic H₂ evolution activity from water for (GaN)_1–x(ZnO)_x without cocatalysts, pH modifiers and sacrificial reagents. Syntheses were carried out by reacting GaN and ZnO in appropriate amounts at temperatures ranging from 1150 to 1200 °C, and at a pressure of 1 GPa. ZnGa₂O₄ was observed as a second phase, with the amount decreasing from 12.8 wt% at x = 0.07 to ∼0.5 wt% at x = 0.9. The smallest band gap of 2.65 eV and the largest average photocatalytic H₂ evolution rate of 2.31 μmol h⁻¹ were observed at x = 0.51. Samples with x = 0.07, 0.24 and 0.76 have band gaps of 2.89 eV, 2.78 eV and 2.83 eV, and average hydrogen evolution rates of 1.8 μmol h⁻¹, 0.55 μmol h⁻¹ and 0.48 μmol h⁻¹, respectively. The sample with x = 0.9 has a band gap of 2.82 eV, but did not evolve hydrogen. An extended photocatalytic test showed considerable reduction of activity over 20 hours.

(GaN)_1–x(ZnO)_x synthesized at high pressure produces H₂ in the presence of visible light without any cocatalysts or sacrificial reagents.     

Improvement in the thermoelectric performance of highly reproducible n-type (Bi,Sb)2Se3 alloys by Cl-doping

(Bi,Sb)₂Se₃ alloys are promising alternatives to commercial n-type Bi₂(Te,Se)₃ ingots for low-mid temperature thermoelectric power generation due to their high thermoelectric conversion efficiency at elevated temperatures. Herein, we report the enhanced high-temperature thermoelectric performance of the polycrystalline Cl-doped Bi_2−xSb_xSe₃ (x = 0.8, 1.0) bulks and their sustainable thermal stability. Significant role of Cl substitution, characterized to enhance the power factor and reduce the thermal conductivity synergetically, is clearly elucidated. Cl-doping at Se-site of both Bi_1.2Sb_0.8Se₃ and BiSbSe₃ results in a high power factor by carrier generation and Hall mobility improvement while maintaining converged electronic band valleys. Furthermore, point defect phonon scattering originated from mass fluctuations formed at Cl-substituted Se-sites reduces the lattice thermal conductivity. Most importantly, spark plasma sintered Cl-doped Bi_2−xSb_xSe₃ bulks are thermally stable up to 700 K, and show a reproducible maximum thermoelectric figure of merit, zT, of 0.68 at 700 K.

Cl-doped Bi_2−xSb_xSe₃ bulks are thermally stable at below 700 K showing a reproducible maximum zT of ∼0.68 at 700 K.     

Uptake of heavy metal ions from aqueous media by hydrogels and their conversion to nanoparticles for generation of a catalyst system: two-fold application study

Poly(methacrylic acid) (P(MAA)), poly(acrylamide) (P(AAm)) and poly(3-acrylamidopropyltrimethyl ammonium chloride) (P(APTMACl)) were synthesized as anionic, neutral and cationic hydrogels, respectively. The synthesized hydrogels have the ability to be used as absorbents for the removal of selected heavy metal ions such as Cu²⁺, Co²⁺, Ni²⁺ and Zn²⁺ from aqueous media. Absorption studies revealed that the absorption of metal ions by the hydrogels followed the order Cu²⁺ > Ni²⁺ > Co²⁺ > Zn²⁺. For the mechanism of absorption, both Freundlich and Langmuir absorption isotherms were applied. Metal ion entrapped hydrogels were treated using an in situ chemical reduction method in order to convert the metal ions into metal nanoparticles for the synthesis of hybrid hydrogels. The synthesis and morphology were confirmed using FT-IR and SEM, while the absorbed metal amounts were measured using TGA and AAS. The hybrid hydrogels were further used as catalysts for the reduction of macro (methylene blue, methyl orange and congo red) and micro (4-nitrophenol and nitrobenzene) pollutants from the aqueous environment. The catalytic performance and re-usability of the hybrid hydrogels were successfully investigated.

Poly(methacrylic acid) (P(MAA)), poly(acrylamide) (P(AAm)) and poly(3-acrylamidopropyltrimethyl ammonium chloride) (P(APTMACl)) were synthesized as anionic, neutral and cationic hydrogels respectively.     

In situ fabrication of porous biochar reinforced W18O49 nanocomposite for methylene blue photodegradation

In this paper, a novel cow dung based activated carbon (CDAC) was successfully modified by W₁₈O₄₉ nanowires as a photocatalyst using KOH activation and a hydrothermal method. The activity of photocatalytic degradation of methylene blue (MB) under full-spectrum light illumination shows great improvement, and the degradation rate of MB could reach 98% after 240 min (67% for W₁₈O₄₉), with a final degradation rate of 98%. The porous structure with specific surface area of CDAC (∼479 m² g⁻¹) increases the adsorption of W₁₈O₄₉ reactants and also raises the concentration of reactants in the photocatalytic region. The high electrical conductivity and good electron storage capacity of CDAC allow the electrons excited in the conduction band (CB) of W₁₈O₄₉ to migrate smoothly into CDAC, which are the keys to enhancing the photocatalytic activity. Moreover, the photocatalytic mechanism was proposed. The results show that the CDAC/W₁₈O₄₉ nanowire composite can be used as an efficient photocatalyst for removal of MB dye from wastewater and indicate remarkable future potential in dye wastewater treatment technologies.

Schematic illustration of the proposed reaction mechanism based on the CDAC/W₁₈O₄₉ composite.     

The rapid microwave-assisted hydrothermal synthesis of NASICON-structured Na3V2O2x(PO4)2F3−2x (0 < x ≤ 1) cathode materials for Na-ion batteries

NASICON-structured Na₃V₂O_2x(PO₄)₂F_3−2x (0 < x ≤ 1) solid solutions have been prepared using a microwave-assisted hydrothermal (MW-HT) technique. Well-crystallized phases were obtained for x = 1 and 0.4 by reacting V₂O₅, NH₄H₂PO₄, and NaF precursors at temperatures as low as 180–200 °C for less than 15 min. Various available and inexpensive reducing agents were used to control the vanadium oxidation state and final product morphology. The vanadium oxidation state and O/F ratios were assessed using electron energy loss spectroscopy and infrared spectroscopy. According to electron diffraction and powder X-ray diffraction, the Na₃V₂O_2x(PO₄)₂F_3−2x solid solutions crystallized in a metastable disordered I4/mmm structure (a = 6.38643(4) Å, c = 10.62375(8) Å for Na₃V₂O₂(PO₄)₂F and a = 6.39455(5) Å, c = 10.6988(2) Å for Na₃V₂O_0.8(PO₄)₂F_2.2). With respect to electrochemical Na⁺ (de)insertion as positive electrodes (cathodes) for Na-ion batteries, the as-synthesized materials displayed two sloping plateaus upon charge and discharge, centered near 3.5–3.6 V and 4.0–4.1 V vs. Na⁺/Na, respectively, with a reversible capacity of ∼110 mA h g⁻¹. The application of a conducting carbon coating through the surface polymerization of dopamine with subsequent annealing at 500 °C improved both the rate capability (∼55 mA h g⁻¹ at a discharge rate of 10C) and capacity retention (∼93% after 50 cycles at a discharge rate of C/2).

NASICON-structured Na₃V₂O_2x(PO₄)₂F_3−2x (0 < x ≤ 1) solid solutions have been prepared using a microwave-assisted hydrothermal (MW-HT) technique.     

Electronic,magnetic, optical and thermoelectric properties of co-doped Sn1−2xMnxAxO2 (A = Mo,Tc): a first principles insight

The electronic, magnetic, optical and thermoelectric (TE) properties of Sn_1−2xMn_xA_xO₂ (A = Mo/Tc) have been examined using density functional theory (DFT) based on the FP-LAPW approach. The results suggested that all the doped compounds show a half-metallic ferromagnet property with a 100% spin polarization at the Fermi level within GGA and mBJ. Moreover, doping SnO₂ with double impurities reduces the bandgap. The reduced bandgaps are the result of impurity states which arise due to the Mn and Mo/Tc doping, leading to the shifts of the minima of the conduction band towards the Fermi energy caused by substantial hybridization between transition metals 3d–4d and O-2p states. Also, the (Mn, Mo) co-doped SnO₂ system exhibits a ferromagnetic ground state which may be explained by the Zener double exchange mechanism. While the mechanism that controls the ferromagnetism in the (Mn, Tc) co-doped SnO₂ system is p–d hybridization. Therefore, the role of this study is to illustrate the fact that half-metallic ferromagnet material is a good absorber of sunlight (visible range) and couples to give a combined effect of spintronics with optronics. Our analysis shows that Sn_1−2xMn_xMo_xO₂ and Sn_1−2xMn_xTc_xO₂ are more capable of absorbing sunlight in the visible range compared to pristine SnO₂. In addition, we report a significant result for the thermoelectric efficiency ZT of ∼0.114 and ∼0.11 for Sn_1−2xMn_xMo_xO₂ and Sn_1−2xMn_xTc_xO₂, respectively. Thus, the coupling of these magnetic, optical, and thermoelectric properties in (Mn, A = Mo or Tc) co-doped SnO₂ can predict that these materials are suitable for optoelectronic and thermoelectric systems.

The electronic, magnetic, optical and thermoelectric properties of Sn_1−2xMn_xA_xO₂ (A = Mo/Tc) have been examined using density functional theory (DFT) based on the FP-LAPW approach.     

Ni stabilized rock-salt structured CoO; Co1−xNixO: tuning of eg electrons to develop a novel OER catalyst

The oxygen evolution reaction (OER) is a key half-reaction in hydrogen–oxygen electrolysers that is very important for efficient electrochemical energy generation, storage and fuel production that offers a clean alternative to fissile fuel combustion based energy systems. Several transition metal containing perovskites were recently explored for the development of superior OER catalysts, and their activity was correlated with the applied potentials at a specific current density to e_g electron density present in the materials. The rock salt structure is envisaged here as a model host structure similar to perovskite to tune the e_g electrons to obtain superior electro-catalytic activity. Incorporation of Ni into CoO lattices helps to stabilize the rock salt structure and modulate the e_g electrons to develop superior OER and ORR electrocatalysts. Nickel doped rock salt structured CoO, Ni_xCo_1−xO (0 ≤ x ≤ 0.5), were synthesized by employing a solid state metathesis synthesis route. The compounds were characterised by powder X-ray diffraction (XRD), TGA, FT-IR and X-ray Photoelectron Spectroscopy (XPS). Ni_0.3Co_0.7O with 1.3 e_g electrons showed superior electrocatalytic activity for the oxygen evolution reaction. The overpotential for the Ni_0.3Co_0.7O sample was also found to be ∼0.450 V for 1 M and about ∼0.389 V at 5 M concentration of the KOH electrolyte.

Incorporation of Ni into CoO lattices helps to stabilize the rock salt structure and modulate the e_g electrons to develop superior OER and ORR electrocatalysts.