Materials Advances最新文献

In this study, four geopolymer composites, GP-0, GP-10, GP-20 and GP-30, were synthesized from pumice, an abundant and inexpensive volcanic rock precursor, substituted with fractions of 0, 10, 20 and 30% by weight of medical waste incinerator fly ash (MWI-FA), respectively. The materials were characterized by standard methods (FTIR, XRF, BET surface area measurement, XRD, SEM-EDX and TGA). The materials were morphologically distinct and the specific surface areas (SSA) decreased with an increase in MWI-FA fraction. The adsorption performances of the geocomposites were evaluated in batch mode for the removal of methylene blue (MB), a toxic dye, from water. The study determined that the dye was optimally removed at circumneutral pH, 303 K temperature, 0.6 g/40 mL adsorbent dosage and 30 min contact time. The equilibrium data were best described using the Sips isotherm model. The geopolymers had ∼30 times higher adsorption capacities than pristine pumice. The maximum adsorption capacities of the geopolymers, ∼31 mg g⁻¹, were indistinguishable despite an increase in MWI-FA indicating that MWI-FA provided new energetically favorable adsorption sites compensating diminished SSA. The adsorption kinetics was best described using the pseudo-second order kinetic model wherein the rate constant (K₂) increased with the MWI-FA fraction suggesting porosity structures with reduced tortuosity. Thermodynamically, the adsorption process was exothermic (ΔH < 0), physical (ΔH and E_a < 40 kJ mol⁻¹) spontaneous (ΔG < 0) and enthalpy-driven. Adsorption diminished in a saline environment. The exhausted adsorbent was recoverable and recycled twice using hot water before significant loss of adsorption potential. The composite geopolymers present a plausible strategy for stabilization of up to 30% MWI-FA without compromising the adsorptive properties for dye removal from water.

Structurally characterized porous spin crossover compounds are attractive types of materials due to their properties that can be regulated under several stimuli, resulting in drastic changes in their optical, electrical, and magnetic responses, leading to potential applications in chemical sensing, memory devices, actuators, etc. In this work, a new 3D Fe^II spin crossover porous coordination polymer, [Fe(tpe)₂dca]ClO₄·5CHCl₃·3CH₃OH (1, tpe = trans-1,2-bis(4-pyridyl)ethene; dca = N(CN)₂⁻), which accommodates guest molecules in its cavities to modulate its magnetic and optical properties, was prepared. 1 was characterized by X-ray diffraction in its fully solvated form by flash cooling single crystals at 100 K, thermogravimetric analysis, elemental analysis and its spin crossover tracked by magnetic susceptibility, and studied by differential scanning calorimetry on single crystals. Compound 1 displays gradual and incomplete spin crossover behaviour with a transition temperature of T_1/2 ∼ 155 K. An optical microscopy study carried out on one single crystal shows an abrupt transition around 180 K with a darkening of the crystal in the low-spin phase, although no clear evidence of an apparent size change was observed. When compound 1 loses its guest molecules partially, [Fe(tpe)₂dca]ClO₄·CHCl₃·2H₂O (2) is obtained in air atmosphere, which is paramagnetic. In addition, the complex [Fe(bpa)₂(NCS)₂]·solvent (bpa = 9,10-bis(4-pyridyl)anthracene, 3) remains paramagnetic down to 100 K, as confirmed by single crystal X-ray diffraction, due to the strong distortion of its octahedral coordination sphere as well as its rigid structure.

Composites possess significant potential to mitigate the shortcomings of their individual components, offering a measure of reinforcement. In this study, composites based on CFA based Na-A and ZIF-8 were synthesized and subjected to CO₂ adsorption tests. The composites were identified as a class of ZIF-8@Na-A. These composites retained the physical attributes of their parent materials. Notably, the CO₂ uptake performance of ZIF-8@Na-A (1 : 5) was particularly high, recording values around 3.48 mmol g⁻¹ at 298 K and 1 bar. Hierarchical three step process optimization has been done to achieve the highest carbon capture and stability. Different synthesis protocols have been compared too. TGA studies have been used to validate the amine loading on the adsorbent. Among the factors influencing CO₂ uptake, temperature and pressure emerged as the most influential, while the time of carbonation exhibited minimal impact. Kinetic analysis revealed that the optimized adsorbent adhered to Avrami kinetics, displaying high R² values of 0.994. The Sips adsorption model demonstrated the best fit for explaining the adsorption behavior of the adsorbents. The average heat of adsorption for ZIF-8@Na-A was measured at −11 kJ mol⁻¹. During a 50-cycle stability assessment, the adsorbent exhibited robust performance, retaining approximately 92% of its initial CO₂ uptake. However, a subtle change in appearance was observed in the ZIF-8@Na-A adsorbent, which turned slightly pale yellowish after the completion of 50 cycles.

Halide and cation engineering of organic–inorganic hybrid perovskites has shown a great potential for structural modulation of perovskites and enhancing their optoelectronic properties. Here, we studied the impact of Cl/Br halide engineering on the structural and piezoelectric properties of MA/Cs mixed-cation Cu-perovskite crystals. X-ray diffraction, Raman spectroscopy, and ¹³³Cs solid-state NMR were utilized to find out the nature of the perovskite crystal structure formation. Three distinct crystal structures were obtained depending on the Cl/Br content. High Cl content resulted in the formation of Br-doped (Cs/MA)CuCl₃ perovskite with the presence of paramagnetic Cu²⁺ ions. High Br content led to the formation of Cl-doped (MA/Cs)₂CuBr₄ perovskite with the presence of diamagnetic Cu⁺ ions. Equimolar Cl/Br perovskite content gave a novel crystal structure with the formation of well-dispersed diamagnetic domains. Compared to the high Cl/Br containing perovskites, the equimolar Cl/Br perovskite revealed the highest potential for piezoelectric applications with a maximum recordable piezoelectric output voltage of 5.0 V. The results provide an insight into the importance of mixed-halide and mixed-cation engineering for tailoring the perovskite structural properties towards a wide range of efficient optoelectronics.

The increasing demand for environmentally friendly materials to address environmental toxicity has prompted a shift towards natural products. This study focuses on the development of biodegradable starch-based (ST) hydrogels modified with gum tragacanth (GT) using polyvinyl alcohol (PVA) as a cross-linker. These hydrogels were utilized as efficient adsorbents for the removal of methylene blue (MB) and congo red (CR) dyes from aqueous solutions. The hydrogels were synthesized via the solution casting method, yielding four variants by adjusting the weights of ST and GT in ratios of ST/GT (2 : 0, 1.5 : 0.5, 1 : 1, and 0.5 : 1.5). Characterization of the hydrogels was performed using FTIR, FESEM, and TGA-DSC. During MB dye adsorption, ST/GT (0.5 : 1.5) exhibited a remarkable removal efficiency of 97.6% within 90 minutes, at pH 10 and an initial dye concentration of 30 ppm. Similarly, for CR dye, the highest removal efficiency of 93.7% was observed with ST/GT (0.5 : 1.5) under optimal conditions of 90 minutes, pH 2, and a dye concentration of 10 ppm. Kinetic studies indicated that the adsorption process followed a pseudo-second order model. Biodegradability tests confirmed the complete breakdown of the hydrogels in soil. This study successfully demonstrates the potential of using plant-based hydrogels for efficient pollutant removal and sustainable water treatment.

The anticancer efficacy of chemodynamic therapy (CDT) is significantly reduced owing to the mild acidic nature of the tumour microenvironment (TME). Typically, Fenton catalysts require a strong acidic microenvironment for effective radical generation at the tumour site. Hence the development of new strategies to achieve efficient Fenton reactions by increasing the acidity of the TME is highly demanded for the advancement of CDT-based cancer treatment. Herein, we demonstrate that the loading of the pH-regulator tamoxifen (TAM) into a CDT nanoagent (DNA1some) could significantly boost the efficiency of CDT action by increasing the acidity at the TME. The integration of nucleolin specific aptamer DNA (DNA2) onto the surface of DNA1some (DNA1some/TAM/DNA2) permitted the targeted internalization of the nanoformulation selectively into cancer cells, and consequently, a very efficient Fenton reaction was demonstrated inside the cancer cells selectively, which reduced the “off-target” toxicity of the nanoformulation to the surrounding normal cells. Enhanced cytotoxicity was observed for the TAM-loaded DNA1some compared to DNA1some and TAM alone, which was attributed to the very efficient Fenton reaction by DNA1some due to the increase in acidity caused by the release of TAM. Hence, the pH-regulator-loaded CDT-active DNAsome can potentially overcome the intrinsically insufficient acidity of the TME for enabling efficient Fenton reactions.

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Developing luminescence sensors often prioritizes maximizing relative sensitivity to achieve optimal performance. However, a critical parameter often overlooked is the temperature at which maximum sensitivity occurs. In this study, we delve into this crucial aspect by exploring the impact of erbium doping in Tm³⁺/Yb³⁺ co-doped Ba₂GdV₃O₁₁ nano phosphors. The crystal structure, microscopic morphology, and luminescence mechanism of BGVO:Yb³⁺/Tm³⁺ and Er³⁺/Tm³⁺/Yb³⁺ up conversion nanoparticles, as well as the temperature sensing characteristics are investigated. Under 975 nm laser excitation, the BGVO:Yb³⁺/Tm³⁺ and BGVO:Er³⁺/Tm³⁺/Yb³⁺ nano phosphors exhibited strong blue and green upconversion luminescence, respectively. The luminescence intensity ratio (LIR) approach was used to analyze the temperature-dependent luminescence spectra in the 300–600 K temperature range. The thermometry strategies were based on thermally coupled energy levels (TCLs) and non-thermally coupled energy levels (NTCLs) of Er³⁺ and Tm³⁺ for temperature sensing performance. In the Tm³⁺/Yb³⁺ codoped samples, the relative sensitivity typically peaks around 350 K, attributed to TCLs (1.7% K⁻¹, 700 nm/800 nm) with generally lower relative sensitivity compared to non-TCLs (5.39% K⁻¹, 700 nm/475 nm). However, non-TCL sensitivities in the 300–600 K range lack a clear maximum. In contrast, Er³⁺/Tm³⁺/Yb³⁺ samples exhibit distinct maxima in non-TCL sensitivities within this temperature range (1.91% K⁻¹, 700 nm/550 nm), offering precise temperature determination for specific applications. Our findings underscore the potential of erbium doping to modulate temperature sensitivity peaks, crucial for optimizing performance in tailored luminescence nanosensors and offering fresh concepts for investigating alternative superior optical temperature sensing nano materials.

Nanosized polymeric vesicles (polymersomes) self-assembled from double hydrophilic copolymers of poly(3-methyl-N-vinylcaprolactam)_n-b-poly(N-vinylpyrrolidone)_m (PMVC_n-b-PVPON_m) using all aqueous media are a promising platform for biomedical applications, because of their superior stability over liposomes in vivo and high loading capacity. Herein, we explored the temperature-sensitive behavior of PMVC₅₈-b-PVPON₆₅ vesicles using transmission electron microscopy (TEM), dynamic light scattering (DLS), atomic force microscopy (AFM), and small-angle neutron scattering (SANS) in response to lowering the solution temperature from 37 to 25, 20, 14 and 4 °C. The copolymer vesicles with an average size of 350 nm at 37 °C were assembled from the diblock copolymer dissolved in aqueous solution at 4 °C. We show that while the polymersome's size gradually decreases upon the temperature decrease from 37 to 4 °C, the average shell thickness increases from 17 nm to 25 nm, respectively. SANS study revealed that the PMVC₅₈-b-PVPON₆₅ vesicle undergoes a gradual structure evolution from a dense-shell vesicle at 37–25 °C to a highly-hydrated shell vesicle at 20–14 °C to molecular chain aggregates at 4 °C. From SANS contrast matching study, this vesicle behavior is found to be driven by the gradual rehydration of PMVC block at 37–14 °C. The shell hydration at 20–14 °C also correlated with the 4.4-fold decrease in the relative fluorescence intensity from vesicle-encapsulated fluorescent dye, indicating ∼80% of the dye release within 12 hours after the vesicle exposure to 14 °C. No significant (<5%) dye release was observed for the vesicle solutions at 37–20 °C, indicating excellent cargo retention inside the vesicles. Our study provides new fundamental insights on temperature-sensitive polymer vesicles and demonstrates that the copolymer assembly into polymersomes can be achieved by decreasing a copolymer aqueous solution temperature below 14 °C followed by solution exposure to ≥20 °C. This type of all-aqueous assembly, instead of nanoprecipitation from organic solvents or solvent exchange, can be highly desirable for encapsulating a wide range of biological molecules, including proteins, peptides, and nucleic acids, into stable polymer vesicles without a need for organic solvents for dissolution of the copolymers that are amphiphilic at physiologically relevant temperatures of 20–37 °C.