Molar Ratio Of Precursors Research Articles

Asphaltene adsorption on MgO, CaO, SiO2, and Al2O3 nanoparticles synthesized via the Pechini-type Sol−Gel method

Basic, amphoteric, and acidic metal oxide nanoparticles including MgO, CaO, SiO2 and Al2O3 were synthesized via the Pechini-type sol–gel process and evaluated for adsorption of two types of asphaltenes (Ap1, Ap2) extracted from two different Iranian crude oils. The adsorbents were characterized by the N2 adsorption–desorption, XRD, FE-SEM, TEM, and EDS and the asphaltene samples were examined using FTIR analysis. The effects of citric acid to metal precursor molar ratio (M), calcination temperature, type of adsorbent, textural properties, adsorption temperature, and regeneration on the adsorbent performance were investigated. The SiO2 nanoparticle with the highest specific surface area and an amphoteric character was an excellent adsorbent capable of removing more than 70% of asphaltene from a model oil with initial asphaltene concentration of 3000 ppm. However, CaO exhibited the highest specific adsorption capacity, indicating that basic sites were active centers for asphaltene adsorption. It was demonstrated that with increasing the calcination temperature, the crystallite sizes of MgO and SiO2 increased and their BET surface areas decreased. The maximum asphaltene adsorption capacities of MgO and SiO2 nanoparticles were obtained at optimal calcination temperatures of 600 °C and 500 °C, respectively. Moreover, the optimum M value for the synthesis of MgO nanoparticle, in terms of asphaltene adsorption capacity, was M = 1, while it was M = 2 (for Ap1) and M = 1 (for Ap2) for SiO2. The adsorption isotherms were best fitted by the Jovanovic model. Moreover, kinetic data for the best adsorbents (MgO and SiO2) were in maximum agreement with the Elovich model. The adsorbents could be easily regenerated by calcination at 600 °C.

Effect of Methylammonium Iodide on the All-solution Prepared Methylammonium Bismuth Iodide Perovskite Solar Cells Performance

The methylammonium bismuth iodide (MBI), a promising lead (Pb)-free perovskite solar cells (PeSC’s) material, is suitable for photovoltaic applications due to less toxic and good stability. Herein, the effect of MAI (methylammonium iodide) on the structural, morphological, optical properties and solar cells performance of bismuth-perovskite solar cells (Bi-PeSC’s) by all-solution processed multi-step spin coating is investigated. The scanning electron microscope (SEM) morphology visually depicts that with the increase of methylammonium iodide (MAI) precursor molar ratio in bismuth (III) iodide (BiI3) x [= [MAI]/([MAI]+[BiI3])] from x=0 to x=0.8, the morphological phase changed significantly. Likewise, the x-ray diffraction (XRD) peak of BiI3 at 12.78o (003) is tremendously changed in the phase and intensity. At the same time, the solar cell performances exhibit gradual increment as increasing the content of MAI in BiI3 and the open circuit voltage (Voc) is exceeded four-times of the minimum MAI molar ratio. The maximum Voc obtained by multilayer Bi-PeSC’s is 0.34V and an efficiency shows an increment up to 0.0037% at MAI molar ratio, x=0.8. In brief, our findings suggested the improvement of Bi-perovskite absorber layer in the future.

Photocatalytic removal of sulfamethoxazole using yeast biomass-derived NixP/biocarbon composites in the presence of dye sensitizer

Photocatalysis represents an environmental-benign approach for organic pollutant treatment. Herein, a photocatalytic system composed of NixP/biocarbon composite as reactive center and erythrosine B (ErB) as sensitizer was constructed for the removal of sulfamethoxazole (SMX) antibiotic under visible light irradiation. NixP/biocarbon composites were fabricated via a facile impregnation-pyrolysis approach using baker’s yeast as both phosphorus and carbon precursor. It was found that NixP with pure Ni12P5, almost pure Ni2P or mixed crystal phases could be obtained by simply adjusting Ni:P molar ratio in precursor and pyrolysis temperature. Interestingly, the variation of NixP crystal phases remarkably affected photocatalytic removal efficiency of SMX. The obtained NixP(1:4)− 900 sample with mixed phases of Ni12P5 and Ni2P displayed excellent photodegradation performance with 98.71% removal efficiency for SMX (C0 = 20 mg L−1) in ErB-sensitized photocatalytic system. Moreover, the reusability of NixP/biocarbon composite was confirmed by four consecutive runs. The slight loss of activity in recycle study could be fully recovered after thermal regeneration. Further investigation indicated that photo-generated electrons from excited ErB molecules could be transferred to NixP/biocarbon, triggering a series of reactions to form various reactive oxygen species (eg., •O2−, H2O2, •OH) for SMX degradation. The better photocatalytic activity of NixP mixed crystal phases should be ascribed to its faster electron transfer ability. Overall, this study provides useful guidance in terms of the development of transition metal phosphide and efficient photocatalytic system.

Pb2+ Responsive Cu-In-Zn-S Quantum Dots With Low Cytotoxicity.

Water-soluble Cu-In-Zn-S quantum dots (CIZS QDs) with orange fluorescence have been synthesized with a glutathione (GSH) as stabilizer via facile a one-step hydrothermal method. The optimal reaction conditions of CIZS QDs including temperature, time, pH, and the molar ratios of precursors were studied. TEM results indicate that the aqueous-dispersible CIZS QDs are quasi-spherical, and the average diameters are 3.76 nm with excellent fluorescent stability. Furthermore, the cytotoxicity of CIZS QDs was investigated by the microcalorimetry combining with TEM and the IC 50 was 10.2 μM CIZS QDs showed a promising perspective in applications such as a fluorescent probe for bioimaging and biolabeling due to the low cytotoxicity and good biocompatibility. Moreover, the CIZS QDs can distinguish Pb2+ ion from other ions, offering great potentials in lead ion determination in drinking water. According to the results of UV, XRD, FL, PL, and ITC methods, the mechanism of CIZS QDs-Pb2+ assay is due to hydrogen bonding or van der Waals forces in the formation of Pb2+ and CIZS QDs.

High-temperature resistant ambient pressure-dried aluminum doped silica aerogel from inorganic silicon and aluminum sources

Aluminum doped silica aerogel (ASA) exhibiting improved high-temperature resistance is usually prepared via supercritical drying from organic silicon and/or aluminum precursors, which propels the production cost significantly. Herein we demonstrate a simple and effective method to prepare highly thermal resistant ASA via the sol-gel and ambient pressure drying route by using water glass and aluminum chloride as precursors. Effects of the Al/Si molar ratio in precursor, the calcination temperature and the modifier type on the crystallinity, morphology, pore structure of ASA are investigated. Results show that the Al/Si molar ratio and the calcination temperature have significant effects on the structure and heat resistance performance of ASA at temperature of 600–1000 °C. The sample with Al/Si molar ratio of 0.15 shows the highest specific surface area of 805.9 m2/g and pore volume of 5.038 cm3/g after heated to 600 °C, and retains 179.5 m2/g and 1.295 cm3/g respectively after heated to 1000 °C. Mechanism analysis indicates that, though the actual aluminum content is extremely low (0.18%, wt%), the high-temperature resistance of ASA is greatly improved owing to the effective doping of aluminum in the lattice of SiO2 and the corresponding electrostatic repulsion between neighboring nanoparticles induced by the replacement of Si4+ by Al3+ ions.

Hydroxyl radical induced from hydrogen peroxide by cobalt manganese oxides for ciprofloxacin degradation

Advanced oxidation processes (AOPs) are promising technology to remove organic pollutant in water. However, the main problem in the AOPs is the low generation of hydroxyl radical (•OH) owing to the low decomposition efficiency of hydrogen peroxide (H2O2). Herein, the spinel type cobalt acid manganese (MnCo2O4) with flower morphology was fabricated through a co-precipitation method. In situ Fourier transform infrared spectroscopy confirms that the MnCo2O4 with the optimal molar ratio of Co and Mn precursors (CM3, Co:Mn = 3) has more Lewis acid sites compared with single metal oxide catalysts (Co3O4 and Mn2O3), leading to the excellent performances for H2O2 decomposition rate constant on CM3, which is about 15.03 and 4.21 times higher than those of Co3O4 and Mn2O3, respectively. As a result, the obtained CM3 shows a higher ciprofloxacin degradation ratio than that of Co3O4 and Mn2O3. Furthermore, CM3 shows an excellent stability during several cycles. This work proposes effective catalysts for ciprofloxacin decomposition and provides feasible route for treating practical environmental problems.

The influence of the precursor molar ratio on the structure of the CdS catalyst during synthesis and visible-light driven CO2 reduction into solar fuel

CdS with a self-assembled nanoflower morphology synthesized using Cd(NO3)2 : CS(NH2)2 = 2 : 1 in ethylenediamine shows the highest performance for CO2 photocatalytic reduction.

Synthesis and characterizations of Mn doped alloyed ZnxCd1-xS nanocrystals

Composition regulation of semiconductors can engineer the band gap and thus tune the optical properties. For effective utilization of orange emitting phosphors in color conversion applications blue excitation is necessary. Here in this work, absorption and photoluminescence spectroscopic measurements have been done to study the variation in band gap energy by changing the composition of ZnxCd1-xS nanocrystals. Further, ternary Mn doped ZnxCd1-xS semiconductor nanocrystals have been synthesized via an aqueous route over a wide composition range by adjusting the molar ratio of precursors which leads to tunable bandgap, thus propagate the progressive growth of light absorption and photoluminescence spectra. The variation in tunability of bandgap is due to the change in Cd/Zn ratio. By changing Cd/Zn ratio excitation wavelength shifts from UV to blue colour. Copyright © 2017 VBRI Press.

Cannabidiol-Mediated Green Synthesis, Characterization, and Cytotoxicity of Metal Nanoparticles in Human Keratinocyte Cells.

This study investigated a unique one-pot microwave-assisted green synthesis method of gold (Au) and silver (Ag) nanoparticles (NPs) using cannabidiol (CBD) as a capping and reducing agent. Furthermore, Au and Ag NPs were also chemically synthesized using poly(vinyl pyrrolidone), which functioned as reference materials when comparing the size, shape, and cytotoxicity of NPs. Synthesis parameters such as reaction time, temperature, and precursor molar ratio were optimized to control the size and shape of the biosynthesized NPs. Various characterization techniques such as transmission electron microscopy, ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction were used to confirm the formation and properties of Au and Ag NPs. Both biosynthesized metal NPs were spherical and monodispersed, with average particle sizes of 8.4 nm (Au-CBD) and 4.8 nm (Ag-CBD). This study also explored the potential cytotoxicity of CBD-capped NPs in human keratinocyte cells, which was observed to be of minimal concern. The novel synthesis approach presented in this study is free from harsh chemical reagents; therefore, these NPs can be used in a wide array of applications, including the pharmaceutical and biomedical fields.

A Novel Sodium-Ion Batteries: Synthesis and Characterization of Nanostructured Sodium Rhodizonate Cathodes

Several studies have emerged that seek to solve the energy deficit that we face as a society, where energy storage plays an important role. In this regard, Ion-Sodium batteries (Ion-Na) represent an excellent alternative to the Ion-Li batteries currently on the market. These new Ion-Na batteries have adequate charge densities and at a lower cost. Taking this issue into account, there is great interest in studying the composition, structure, and morphology of cathodes as active materials to optimize this type of battery. [i],[ii] .In this study, the synthesis and characterization of sodium rhodizonate nanostructures to be used as cathode material in Sodium-ion batteries was carried out. In a first stage, a two-level factorial design was used as an exploratory stage to evaluate the statistical significance of the variables involved in the synthesis: i) temperature, ii) reaction time, iii) molar ratio of precursors, and iv) addition time. The nanostructuring of the sodium rhodizonate crystals was carried out by the ultrasonic crystallization method and was characterized by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The electrochemical characterization was performed using cyclic voltammetry, galvanostatic charge/discharge profiles, and cyclability. The results show that the nanostructuring of the material causes an increase in the storage capacity of sodium ions in the sodiation/desodiation process. This shows a strong size-dependence in the Na + ion intercalation process. Finally, these results will allow the generation of causal relationships that lead to the optimization of the electronic properties of alternative Na-ion batteries. [i] Minah Lee, Jihyun Hong, Jeffrey Lopez, Yongming Sun, Dawei Feng, Kipil Lim, William C. Chueh, Michael F. Toney, Yi Cui & Zhenan Bao. Nature Energy, volume 2, pages 861–868 (2017). [ii] R.-E. Dinnebier, H. Nuss, M. Jansen, Disodium rhodizonate: a powder diffraction study, Acta Crystallographica E61 (2005) m2148–m2150.

Fabrication of vibration sensors using precursor molar concentration varied ZnO nanostructures grown by refresh hydrothermal method

PurposeVarious approaches have been made to alter the vibration sensing properties of zinc oxide (ZnO) films to achieve high sensitivity. This paper aims to report the experimental study of the fabrication of precursor molar ratio concentration varied ZnO nanostructures grown on rigid substrates using the refresh hydrothermal method. The effect of these fabricated ZnO nanostructures-based vibration sensors was experimentally investigated using a vibration sensing setup.Design/methodology/approachZnO nanostructures have been grown using low temperature assisted refresh hydrothermal method with different precursor molar concentrations 0.025 M (R1), 0.075 M (R2) and 0.125 M (R3). Poly 3,4-ethylenedioxythiophene polystyrene sulfonate, a p-type material is spun coated on the grown ZnO nanostructures. Structural analysis reveals the increased intensity of the (002) plane and better c-axis orientation of the R2 and R3 sample comparatively. Morphological examination shows the changes in the grown nanostructures upon increasing the precursor molar concentration. The optical band gap value decreases from 3.11 eV to 3.08 eV as the precursor molar concentration is increased. Photoconductivity study confirms the formation of a p-n junction with less turn-on voltage for all the fabricated devices. A less internal resistance of 0.37 kΩ was obtained from Nyquist analysis for R2 compared with the other two fabricated samples. Vibration testing experimentation showed an improved output voltage of the R2 sample (2.61 V at 9 Hz resonant frequency and 2.90 V for 1 g acceleration) comparatively. This also gave an increased sensitivity of 4.68 V/g confirming its better performance when compared to the other fabricated two samples.FindingsPhotoconductivity study confirms the formation of a p-n junction with less turn-on voltage for all the fabricated devices. A less internal resistance of 0.37 kΩ was calculated from the Nyquist plot. Vibration testing experimentation proves an increased sensitivity of 4.68 V/g confirming its better performance when compared to the other fabricated two samples.Originality/valueVibration testing experimentation proves an increased sensitivity of 4.68 V/g for R2 confirming its better performance when compared to the other fabricated two samples.

Facile controlled formation of CoNi alloy and CoO embedded in N-doped carbon as advanced electrocatalysts for oxygen evolution and zinc-air battery

Constructing Schottky barrier of alloy/metal oxide interfaces is an emerging approach to design electrocatalysts with desired performance. Herein, a nitrogenous organic modified bimetal layered hydroxide salts (LHS) precursor is used to prepare CoNi alloy and CoO coupled nitrogen-doped carbon (NC) hybrids on carbon paper (CP) via a one-step pyrolysis at only 500 °C. Through adjusting the metal molar ratio in LHS precursor and the pyrolysis temperature, CoO is in-situ produced during pyrolysis. Since both alloy and metal oxide possess potential oxygen evolution reaction activity, the resulting CoNi-CoO@NC/CP exhibits enriched electrochemical active surface area, small overpotential (309 mV) at current density of 10 mA cm−2, low Tafel slope (67.7 mV dec−1), and good durability for 64 h at ∼20 mA cm−2 in 1.0 M KOH. Furthermore, a zinc-air battery based on this catalyst shows a high specific power of 96.2 W gcat−1, which exceeds that of conventional RuO2+Pt/C catalyst (66.8 W gcat−1). This work provides an appealing approach for the development of highly efficient alloy/metal oxide electrocatalysts for rechargeable metal-air battery.

Formation of organic chloramines during chlorination of 18 compounds

Organic chloramines have attracted considerable attention because of their potential toxicity and reactivity. However, the lack of suitable and effective analytical methods has limited the study of organic chloramines due to their volatile and unstable properties. In this study, membrane introduction mass spectrometry (MIMS) combined with DPD/FAS titration was used to monitor the formation of organic chloramines. N-chlorodimethylamine [(CH3)2NCl] and N-chlorodiethylamine [(C2H5)2NCl] were detected and identified as the dominant volatile DBPs during chlorination of 18 organic compounds with dimethylamine or diethylamine functional groups, with yields ranging from 0.3% to 51.1% at a chlorine to precursor (Cl/P) molar ratio of 8.0. (CH3)2NBr was formed in the presence of bromide, while the formation of (CH3)2NCl was decreased. The reaction of phenol with (CH3)2NCl combined with theoretical calculations confirmed that the reactivity of (CH3)2NCl was similar to that of monochloramine. Moreover, (CH3)2NCl and (C2H5)2NCl were observed at the ppb level during chlorination of actual water samples collected from different areas. The results suggest that (CH3)2NCl and (C2H5)2NCl are important organic chloramines during chlorination, which may lead to the occurrence of further oxidation reactions and promote the formation of other disinfection byproducts simultaneously and should be of concern.

Irregularly Shaped Bimetallic Chalcogenide Ag8SnS6 Nanoparticles as Electrocatalysts for Hydrogen Evolution

Bimetallic chalcogenides, with several excellent properties, have been reported to be promising electrocatalysts for the hydrogen evolution reaction (HER) in the past few years. Hence, it is of great interest to develop more bimetallic chalcogenides in the relevant fields. Herein, Ag8SnS6 nanoparticles with different Ag/Sn ratios have been synthesized by adjusting the precursor molar ratio via a facile hydrothermal method, among which the sample obtained at SnBr2/AgNO3 = 1/6 exhibits the best performance for HER. After coupling with carbon nanotubes (CNTs), the catalytic performance of Ag8SnS6 nanoparticles can be improved significantly owing to the enhanced charge transport. The resultant Ag8SnS6 + CNT composite shows efficient electrocatalytic activity and good stability for HER in an acid solution. This study reveals the electrocatalytic performance of Ag8SnS6 nanoparticles in HER for the first time and provides a useful guide for the optimization of an HER electrocatalyst.

Composition-Controlled Synthesis of Near-IR-Light-Emitting Ag-Ιn-Ga-Se Nanocrystals for Biological Imaging

Colloidal semiconductor nanocrystals have been intensively developed for the application to photovoltaics, light-emitting diodes, electroluminescent device, and photoluminescent markers for bio-imaging. Recently, low-toxic I-III-VI semiconductor-based multinary chalcogenide nanocrystals have attracted much attention as a promising alternative for Cd-based ones, because these nanocrystals are composed of less-toxic elements and exhibited intense photoluminescence (PL) in the visible and near-IR wavelength regions. In our previous paper, we reported that chemically synthesized Zn-Ag-In-S nanocrystals exhibited a broad PL peak (FWHM > 100 nm) originating from donor-acceptor pair radiative recombination, the wavelength of which was tunable from ca. 500 to 800 nm by changing the particle size and the chemical composition.[1] However, these multinary nanocrystals did not exhibit a band-edge emission, though narrowing PL peak has been earnestly desired for luminescent applications. In this study, we report the preparation of novel multinary Ag-In-Ga-Se nanocrystals via solution phase synthesis and control the peak wavelength of band-edge emission in the range from visible to near-IR lights. We also demonstrated the usefulness of thus-obtained Ag-In-Ga-Se nanocrystals for in vivo bio-imaging.[2] Semiconductor nanocrystals composed of Ag-In-Ga-Se (AIGSe) solid solution were prepared by the thermal decomposition of corresponding metal salts and selenourea in a hot mixture solution of oleylamine/1-dodecanethiol under an N2 atmosphere. The molar ratios of precursors were varied with the synthesis of Ag0.67InyGa(1-y)Se2 (AIGSe) in mind. The individual XRD peaks of thus-obtained AIGSe nanocrystals were located between those of tetragonal AgInSe2 and AgGaSe2 crystal structures and shifted to a higher angle with a decrease in the y value, indicating that the Ga3+ fraction in the Ag(In,Ga)Se2 solid solution increased with a decrease in the y value in preparation. TEM measurements revealed that spherical nanocrystals were formed, the average size of which were varied in the range of 3~5 nm depending on the chemical composition. The PL spectra of as-prepared AIGSe nanocrystal exhibited both a narrow band-edge emission peak and a broad defect-site emission peak. By surface-coating AIGSe nanocrystals with GaSx (AIGSe@GaS x ), a broad PL peak was remarkably diminished especially for y = 0.25-0.5, owing to the removal of the surface defect sites. With a decrease in the y value, that is, with an increase in the Ga/In ratio of nanocrystals, the peak wavelength of band-edge emission of AIGSe@GaS x nanocrystals was blue-shifted from 890 to 610 nm because of the increase in their energy gap. The PL quantum yield (QY) was enlarged by the GaS x shell coating, in which the maximum PL QY of 38% was obtained for the PL peak at 800 nm AIGSe@GaS x of y = 0.7. Thus-obtained nanocrystals were successfully used as near-IR PL probes for three-dimensional in vivo bioimaging, in which the wavelengths of excitation and detection lights could be selected in the first biological window. The imaging signals were clearly detected from AIGSe@GaS x nanocrystals injected into biological tissues by ca. 5 mm in depth. Reference Torimoto, et al., J. Phys. Chem. C, 2015, 119, 24740-24749. Torimoto, et al., ACS Appl. Nano Mater . 2020, 3, 3275-3287.

Lamellar Enzyme-Metal–Organic Framework Composites Enable Catalysis on Large Substrates

Lamellar Enzyme-Metal–Organic Framework Composites Enable Catalysis on Large Substrates

Binder-free NiCoFe layered double hydroxide nanosheets for flexible energy storage devices with high-rate-retention characteristics

In this study, NiCoFe layered double hydroxide (LDH) nanosheets with various composition ratios are synthesized via a simple electrodeposition method. The NiCoFe LDH prepared with a precursor molar ratio of Ni:Co:Fe = 1:2:0.1 shows the best performance with a specific capacity of 727 C g − 1 at 1 A g − 1, a high rate retention of 77% at 50 A g − 1, and a capacity retention of 87% after 10,000 cycles. The quick in-operando X-ray absorption study shows that the electrochemical activity of the various LDHs mainly originates from the change in the valence state of Ni ions, and the Fe ions improve the rate capability as well as the cycling stability. Furthermore, a solid-state energy storage device is fabricated using the NiCoFe-(1:2:0.1) LDH as the positive electrode, commercial activated carbon as the negative electrode, and PVA-KOH as the electrolyte. The device exhibits an energy density of 8.7 Wh kg−1 at 62.8 W kg−1 and 6.8 Wh kg−1 at 3139.2 W kg−1. The cycling stabilities of the device under folding and unfolding conditions are also evaluated, and the performances are found about the same, revealing great potential for flexible energy storage applications.

Facile Chemical Processing of Geloina coaxans Shell and Sodium dihydrogen Phosphate as Precursors to Produce Hydroxyapatite

This paper reports the synthesis of hydroxyapatite from Geloina coaxans shell and sodium dihydrogen phosphate as precursors by facile and simple method. Firstly, Geloina coaxans shell calcined at 1000 oC for 12 hours to produce lime or CaO. The chemical composition of Geloina coaxans shell calcined was analyzed using the XRF technique, and the result shows that the main component of Geloina coaxans shell calcined was calcium. Synthesis of hydroxyapatite has been done with stirring and aging time parameters and molar ratio of precursors was 1.67. The XRD patterns showed a specific peak of hydroxyapatite that appeared at 2θ=31.8 o and based on the XRD results on the aging time indicated that the rate of growth of HAp crystals was better and faster at aging for 12 hours. The crystal size of HAp obtained was 37 nm. The FTIR spectra of hydroxyapatite showed characteristics of hydroxyl and phosphate bands in sample spectra. The morphology of hydroxyapatite synthesized also was examined by SEM and the results showed spherical morphology.

Improving the crystallinity of CH3NH4PbBr3 single crystal thin films via controlling the evaporation of methylamine

Halide perovskite single crystal thin films (SCTFs) have attracted extraordinary attentions due to the promising potential applications as the high-performance optoelectronic devices. However, fabricating the high-quality and large-area perovskite SCTFs is still the main challenge for the future commercialization. In this work, systematical investigations show that the evaporation of methylamine can lead to the precipitation of the PbBr2 phase, which is one of the major causes of the poor crystallinity and the surface morphology. A simple strategy is demonstrated to improve the crystallinity and properties of MAPbBr3 SCTFs using the mainstream space-confined method, by controlling the evaporation of the methylamine during the crystal growth, i.e. the growth temperature and the PbBr2/MABr molar ratio in precursor. The crystal quality of MAPbBr3 SCTFs can be improved by lowering the growth temperature and decreasing the PbBr2/MABr molar ratio in the precursor. The best MAPbBr3 SCTF is obtained at 50 °C with the PbBr2/MABr molar ratio of 0.85 in precursor solution. The SCTF is in square shape (~2 mm × 2 mm) and with a full width of half-maximum of the rocking curve of (100) crystal plane of 0.051o. These results will inspire the further explorations in fabricating the high-quality perovskite SCTFs.

Impact of the size effect on enzymatic electrochemical detection based on metal-organic frameworks

Metal-organic frameworks (MOFs) hold a great promise as immobilization carriers for enzymes and other biomolecules, owing to their enhanced stability, selectivity and controllability. However, enzyme-MOF complexes usually lead to a decrease in the apparent enzyme activity and apparent substrate affinity as a result of the constrained structure of the enzyme and the mass transfer limitation of the substrate, respectively. These results consequently impede the applications of enzyme-MOF complexes in biocatalysis and biosensing. In this study, zeolitic imidazolate framework-8 (ZIF-8) was synthesized to immobilize cytochrome c (Cyt c) via a one-step co-precipitation process under mild conditions. By adjusting the molar ratio of precursors, enzyme-MOF composites with different sizes from 100 nm to 1.3 μm were prepared. The decreased size of the prepared MOFs generated an increase in substrate affinity (with an over 50% decrease in the Michaelis constant Km) and a 6.4-fold improvement in the apparent enzyme activity with a 6.26-fold increase in the enzymatic electrochemical detection sensitivity compared with native Cyt c. The enzyme-MOF composites were coated on a screen-printed electrode for the sensitive and fast detection of H2O2, which is the most common representative of reactive oxygen species in cellular environments, showing the potential for the construction of efficient biosensors with applications in biomedicine.