Wet Chemical Technique Research Articles

A comparison of in vitro cytotoxicity of undoped and doped surface modified CaS nanoparticles

In the present study we compare the cytotoxicity of undoped and doped surface modified CaS nanoparticles synthesized by wet chemical co-precipitation technique using L929 human fibroblasts cell lines. The toxicity was determined by evaluating the cell viability and changes in cell morphology. In addition, the half-maximal inhibitory concentration (IC50) values for all the samples were also compared. This analysis shows that undoped and terbium doped TEOA capped CaS nanoparticles are more biocompatible and will be better candidates for various applications in the biomedical field.

Enhanced magnetic performance in exchange-coupled CoFe2O4–LaFeO3 nanocomposites

Nanocomposite oxide system of (x)CoFe2O4–(100-x)LaFeO3 with different weight percent of core-shell structured CoFe2O4 (x = 0, 20, 40, 50, 80, 100) and LaFeO3 were fabricated, via a two-step sol-gel wet-chemical synthesis technique. The phase formation of the composites was confirmed by x-ray diffraction and the structural parameters of both the phases were attained from the Rietveld refinement results of XRD patterns. The elemental composition and microstructure of the resulting nanocomposites were examined by using energy-dispersive x-ray spectroscopy and high-resolution transmission electron microscopy technique, respectively. The detailed magnetometry studies at 300 K and 5 K reveal that the inter-and intra-phase magnetic interactions affect the saturation magnetization (M S), remanence magnetization (M R) and coercivity (H C) values of this bi-magnetic system. The remarkable feature of ‘pinched magnetic hysteresis loop’ was evidenced in the [(50) CoFe2O4 - (50)LaFeO3] composite, leading to a lesser magnetic loss factor and better magnetic performance of this sample. The report depicts an improved interfacial exchange coupling at 5 K, for the nanocomposites of core-shell morphology and offers an understanding or explanation of improved magnetic performance for the (50)CoFe2O4 - (50)LaFeO3 nanocomposite and opens up an important way to design new multiferroic applications in low magnetic fields.

Synthesis of La1-xGdxFe1-yCoyO3/r-GO nanocomposite with integrated features for the treatment of hazardous industrial effluents

Solar-light triggered semiconductive materials with a small bandgap, a low electron-hole pair recombination rate, and quicker charge carrier characteristics are very efficient catalysts for hazardous industrial effluent treatment. Herein, we adopted wet-chemical and ultra-sonication techniques to prepare binary metal (Gd & Co) doped Lanthanum ferrite (GCLFO) nanoparticles and their reduced-graphene (r-GO) based nanocomposite (GCLFO/r-GO) as an ideal photocatalyst. The binary metal doping and composite formation strategies were adopted primarily to facilitate the electronic excitation and accelerate the charge transport characteristics of the finally obtained photocatalyst. Prepared solid samples were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), Raman, Fourier transform-infrared (FT-IR), current-voltage (I–V), BET (Brunauer, Emmett, and Teller), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy. An improvement in the photo-degradation of Phenol Red (PR) dye by GCLFO/r-GO nanocomposite was observed. The increased photocatalytic activity of the GCLFO/r-GO nanocomposite is primarily a result of doping, nanotechnology, and composite formation strategies. These strategies tune the bandgap of the nanocomposite sample, increase its surface area, and decrease its electrical resistivity. Highly encouraging photocatalytic findings suggest that using multiple strategies to prepare an ideal photocatalytic material with integrated features is a very efficient approach.

One-pot synthesis of carbon-supported AuCo and AuNi nanoalloys for the oxygen reduction reaction in alkaline media

Carbon-supported bimetallic AuCo and AuNi electrocatalysts were prepared from one-pot wet-chemistry techniques (ethylene glycol-stabilization and aqueous-solution stirring) and evaluated for the oxygen reduction reaction (ORR) in alkaline media. All the materials consist of near-spherical nanoparticles that show varying sizes and extent of agglomeration. While the ethylene-glycol method produced less agglomerated particles, the stirring method produced smaller ones. X-Ray photoelectron (XPS) analyses demonstrated the change in the binding energies of Au 4f5/5 and Au 4f7/2 versus the expected values for pure gold, pointing at the formation of alloyed nanoparticles. The combination of such electronic effects and morphology led the AuNi/C-EG nanoalloy to a good compromise between materials cost (versus Au/C) and ORR activity: the onset potential and half-wave potential for the oxygen reduction reaction are 0.833 and 0.600 V vs. RHE, respectively, corresponding to a specific activity 10% greater than that for Au/C at 0.85 V vs. RHE. The carbon-supported AuNi nanoalloy possesses undoubtable potential to be used as an electrocatalyst for the electroreduction of oxygen in alkaline environments.

A new empirical approach for rapid quantification of organic and pyritic sulfur in sedimentary rocks using the Rock-Eval 7S

Evaluation of individual sulfur (S) fractions in sedimentary rocks (e.g., pyrite, organic-S) provides essential information about paleo-environmental conditions of sediment deposition and petroleum systems characteristics. However, measuring organic- and pyritic-S concentrations involves tedious and time-consuming (days per sample) wet chemistry techniques. A more tractable approach uses gradual heating of the rock to separate the S-fractions according to their different thermal stabilities. Such an approach is implemented here using the newest Rock-Eval model (RE-7S, Vinci Technologies), which allows monitoring of the S products during gradual heating in sequential pyrolysis and combustion cycles. The rapid (∼1 h per sample) analysis differentiates between the peaks of pyrolyzed organic- and pyritic-S. However, the residual S of both organic and pyritic fractions is decomposed at the same temperature range during combustion, challenging their quantitative separation. Here we suggest an empirical approach to separate the S-fractions based on a linear correlation (R2 = 0.98, n = 9) between two new defined parameters: the relative amount of pyrolyzed organic-S (PyOS %) to the temperature at maximum organic-S elution during pyrolysis cycle (Tmax-S °C). The correlation was common to nine source rocks, including Types I, II, and II-S kerogens, varied S concentrations (0.8–8.7 wt%), and different mineral matrices (carbonates, siliceous). The average precision achieved by the approach was 6% relative standard deviation for replicate measurements. Accuracy was mostly within 10% compared with the values determined by the conventional wet-chemistry technique. This new empirical approach provides a rapid and robust method for quantifying organic and pyritic sulfur in sedimentary rocks.

Synthesis of n‐HAP using different precursors and dependence of Vickers hardness on the structure by tuning sintering temperature

AbstractThree sets of starting materials Ca(NO3)2·4H2O and (NH4)2HPO4; Ca(OH)2 and H3PO4; Ca(OH)2 and (NH4)2HPO4 were chosen for the preparation of different precursors of hydroxyapatite nanoparticles (n‐HAP) by wet chemical precipitation technique denoted by HAP‐1, HAP‐2, HAP‐3. X‐ray diffraction (XRD) studies show that n‐HAP of all three types exhibited single‐phase in the as‐prepared condition. Transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED) studies of as‐prepared samples showed characteristic needle‐like particles with a width of 5 nm, which were fully crystalline exhibited by the lattice fringe in HRTEM, and single‐phase demonstrated by SAED patterns. The samples were pelletized and annealed at varying temperatures in the range of 600°C–1400°C. The results indicated that HAP‐1 and HAP‐3 samples showed phase decomposition at 1400°C to form β‐tricalcium phosphate (β‐TCP) while for HAP‐2 no such decomposition occurred up to 1400°C. Data from the Vickers hardness test revealed that the hardness value up to 2.5 GPa was attained at the sintering temperature of 1200°C for HAP‐1 and HAP‐3. The hardness values are consistently higher for HAP‐2 than HAP‐1 and HAP‐3 at all sintering temperatures and attained a value of 3 GPa at 1200°C. Thus, synthesizing n‐HAP by using H3PO4; Ca(OH)2 bestows highest Vickers hardness.

Significantly reduced leakage current density in Mn-doped BiFeO3 thin films deposited using spin coating technique

BiFeO3 (BFO) and Mn-doped BFO thin films are prepared on indium tin oxide/glass substrates using wet chemical deposition technique. The role of Mn defects (3% to 10%) on the leakage current density and other physical properties of BFO thin film devices is investigated. The X-ray diffraction patterns confirm the single-phase formation of rhombohedrally distorted BFO thin films. The scanning electron microscopy images approve uniform and crack-free film depositions, which is of great importance to the practical device applications of such materials. The oxidation states are determined by X-ray photoelectron spectroscopy (XPS). These XPS results reveal the presence of multiple valence states of Fe ions (Fe2+, Fe3+) and Mn (Mn3+, Mn4+) ions, which play a decisive role in determining the leakage current density. However, the Mn-doping at the Fe site in BFO reduces oxygen vacancies and Fe2+ states, hence suppressing the leakage current density. The leakage current density is reduced by three orders of magnitude (10−4 – 10−7) A/cm2, upon Mn-doping as clearly demonstrated by J-V characteristics. These results indicate that the primary contributors to the conduction in BFO based thin films are oxygen vacancies and the Fe2+ states in these devices.

Synthesis and Characterization of Nitrogen Doped Reduced Graphene Oxide Based Cobalt-ZIF-8 Catalysts for Oxygen Reduction Reaction

Non-Platinum Group Metal (non-PGM) catalysts have recently attracted huge attention for use in the Polymer Electrolyte Membrane Fuel Cell (PEMFC) vehicles, as the demand for alternative and sustainable transportation is increasing exponentially. Carbon-based catalysts have advantages such as relative ease of manufacturing, low cost of synthesis, high electrochemical durability, and high electrical conductivity which makes them a potential alternative. While there are several ways to improve the catalytic activity of carbon catalysts, one promising technique is doping heteroatoms into the lattices of the sp2 carbon structure. The most commonly used doping is by nitrogen (N-doping) where a nitrogen precursor is used to incorporate N atoms to help improve electrochemical performances. Transition Cobalt-Nitrogen-Carbon (Co-N-C) catalysts show promising catalytic performance and durability due to their fast electron transfer rates leading to increased kinetic reaction rates. In this paper, we report the synthesis and characterization of Nitrogen-doped Graphene/Graphene oxide with Metal-Organic Framework (MOF) material using wet chemical and pyrolysis techniques for the development of an efficient catalytic material to tackle the sluggish cathodic Oxygen Reduction Reaction (ORR) in fuel cells (FCs). Transition metal, Cobalt is doped into Zeolite Imidazole Frameworks (ZIF-8) using Cobalt Nitrate as precursor to enhance the mass and kinetic rates of the ORR reaction at the cathode. The synthesized metal-doped MOF catalysts (Co-ZIFx) are further pyrolyzed by one-step pyrolysis in an argon atmosphere at 600oC for 2 hours. These catalysts are produced with varying amounts of precursor metals (different molar ratios of metal precursor to ZIF-8 such as 0.6, 0.9 and 1.2 respectively; x denotes molar ratio values) to analyze the effects of each element proportion on the electrochemical performance. The pyrolyzed electrocatalysts (named Co-ZIFx-600 respectively) were further synthesized chemically using nitrogen-doped graphene (N-Gr) catalysts through wet chemical synthesis procedure and are named as N-Gr-Co-ZIFx and N-Gr-Co-ZIFx-600 (x changes with the molar ratios of metal precursor). Doping of graphene carbon lattice with nitrogen heteroatoms has proven to influence charge densities and adsorption mechanism which further enhances the catalytic activity. Nitrogen loading effects were also analyzed to study the electronic and electrochemical behavior of individually varied graphene materials. Various characterization techniques, viz., FTIR, Raman spectroscopy, XRD, SEM and EDS were performed to analyze various physical and chemical properties affecting the electrochemical performances. FTIR of N-Gr-Co-ZIF-600 catalysts showed the presence of cobalt-doped ZIF-8 peaks around 420 cm-1 and the presence of nitrogen bonds at a stretching frequency of around 3000 cm-1. XRD results showed the formation of crystalline phases of the Cobalt-doped ZIF-8 with a (100) orientation. Further, it was observed that the crystallinity was affected with an increase in the metal loading. SEM examination of the Cobalt-doped ZIF-8 samples showed an increase in grain size from around 100 nm to 2 μm with an increase in cobalt composition. EDS results of the catalysts indicated uniform distribution of the various elements such as carbon, nitrogen, cobalt, oxygen, and zinc (from ZIF-8) in varying proportions as we alter the metal precursor doping in ZIF-8. Cyclic Voltammetry is performed in 0.1M HClO4 aqueous solution to evaluate the electrochemical performances of the synthesized catalysts. It is found that the addition of the transition metal plays a major role in the enhancement of electrochemical performance compared to that of non-transition metal carbon-based catalysts. the N-Gr-Co-ZIFx-600 catalyst showed relatively better ORR activity in acidic media with onset and half-wave potentials only 24 and 51 mV lower than those of the Pt/C catalyst. Overall, the synthesized N-Gr-Co-ZIFx-600 is a potential candidate as a high activity, stable, and low-cost ORR catalyst for FCs. All the results of the characterizations will be discussed in detail for different metal precursor loadings (0.6, 0.9 and1.2 molar ratios) of different MOF derived carbon-based electrocatalysts.

Preparation of Efficient Memristive Films (2D materials) for Flexible Devices and Their Electrical Characterisation

2D materials have various properties that make them potential candidates for better applications in electronic, chemical and biosensing devices. Indisputably, so much work have been done on 2D materials. However, the aim of this study is to fabricate a material with a better quality that is capable of creating room for greater opportunities in electronic, chemical and biosensing devices. Thus, in this study, fabrication was performed through exfoliation, and wet chemical means or PVD layer deposition technique. Furthermore, the current state of the electronics industry has necessitated the need for a novel and suitable memory for low cost and large scale flexible electronics materials. These materials should be non-volatile and low-power consuming devices because energy is of global concern. The non-volatility nature and the energy consuming ability of the finally fabrication was investigated from the current vs time curve in order to obtain the energy retention time. After the fabrication of the electronics material, various characterisations were performed on the devices; stability and endurance level was tested from the current vs cycle numbers of the curves. The rationale for these experiments is to take advantage of the Van der Waals multilayer force present in-between the layers of the two-dimensional (2D) materials to form a material with a desirable atomic and accurate quality. The outcome shows an improved 2D memeristive material required to address most challenges experienced by electronic devices, particularly in the multilayer thin film. The result shows performance improvement of the memristors by raising the switching endurance at an elevated temperature of 300 oC and above. Finally, the mechanical flexibility and stability together with its endurance level were tested.

Atomic Layer Deposition for Modification of Various 1D Nanomaterials

One-dimensional nanomaterials – materials with one dimension outside the nanoscale, further noted as 1D NMs – represent a class of very important nanomaterials with continuously increasing importance. Due to their intrinsic features, unique properties and diversity of functionalities, they count among the most widely studied materials nowadays. While considerable research efforts have been spent to synthesize various 1D NMs (e.g. nanopores, nanotubes or nanofibers), limited efforts have been devoted to surface modification and property tailoring of these materials.However, it is their surface that comes into direct contact with various media (air, gases, liquids, solids) and influences the reactivity, stability and biocompatibility of these materials. The surface and aspect ratio (defined as their diameter to length ratio) influence the performance of these materials in various applications. Considering these facts, it is more relevant to tailor the surface of these materials and to be able to influence their properties and reactivity at the nanoscale, rather than to deal with tailoring their own bulk material composition.The focus of this presentation is on the modification of two types of 1D nanomaterials – nanotubes and nanofibers. Numerous techniques can be utilized for this purpose, such as for example wet chemical or physical deposition techniques. However, it is only the Atomic Layer Deposition (ALD) that is capable of really uniform and homogenous coating of these 1D nanomaterials, in particular those of very high-aspect ratio.The presentation will be mainly focused on modification of TiO2 nanotube layers and various nanofibers of different aspect ratios via ALD.Experimental details and some very recent application examples [1-9] and structural characterizations of these modified materials will be discussed. Sopha et al (2017), Appl. Mater. Today, 9, 104.Sopha et al. (2018), Electrochem. Commun., 97, 91.Ng et al. (2017), Adv. Mater. Interfaces, 1701146.Dvorak et al. (2019), Appl. Mater. Today, 14, 1.Sopha et al. (2019), FlatChem 17, 100130.Motola et al. (2019), Nanoscale 11, 23126.Ng et al. (2020), ACS Appl. Mater. Interfaces, 12, 33386.Motola et al. (2020) ACS Appl. Bio Mater. 3, 6447.Rihova & M. Knez & J. M. Macak et al. (2021), submitted

A disposable modified screen-printed electrode using egg white/ZnO rice structured composite as practical tool electrochemical sensor for formaldehyde detection and its comparative electrochemical study with Chitosan/ZnO nanocomposite

In this study, Chitosan/ZnO nanocomposite (Ch/ZnO) and egg white/ZnO rice structured composite was synthesized by simple wet chemical technique and characterised by various techniques. A comparative electrochemical analysis were carried out and determined that egg white/ZnO rice structured composite modified screen printed electrode (SPCE) showed good electrochemical behaviour. The electrochemical activity of egg white/ZnO rice structured composite SPCE was investigated for the oxidation-reduction of formaldehyde in alkaline media using cyclic voltammetry (CV).Their unique electrocatalytic activity for the formaldehyde found to exhibit 254 mV cathodic current response towards low negative potentials. Based on these results, a novel screen printed sensor (Egg white albumin/ZnO rice structured composite) for the determination of formaldehyde was analysed using differential pulse voltammetry (DPV). The sensor response was linear from 0.001 mM to 0.005 mM with limit of detection (LOD) 6.2 nM and their sensitivity was found to be 770.68 mM/μA. The developed electrochemical formaldehyde sensor was successfully applied as working electrode in cyclic voltammetric determination of formaldehyde in urine samples. The sensor is selective, inexpensive, stable over several days and disposable as well as simple to manufacture and operate. The system described here can be easily be adapted to other substrates and used as practical tool for formaldehyde analysis.

Recovery of phosphorus from sewage sludge ash: Influence of incineration temperature on ash mineralogy and related phosphorus and heavy metal extraction

Phosphorus (P) can be effectively recovered from sewage sludge ash (SSA) by applying wet chemical extraction techniques. However, considerable amounts of heavy metals can be co-extracted depending on the type of extraction liquid used. In this study, the influence of the incineration temperature on the ash mineralogy and related P and heavy metal extraction using sulfuric acid, hydrochloric acid, oxalic acid and sodium hydroxide was studied. Results showed that the P extraction efficiency with sodium hydroxide decreased with increasing incineration temperature, related to a decrease in Al/Fe-phosphates in the SSA. Furthermore, P extraction efficiency for the acidic extraction liquids reached a maximum for SSA obtained around 850 °C (> 86% P extracted). Heavy metal co-extraction generally decreased with increasing incineration temperature, which could be linked to the immobilization of the heavy metals in the SSA matrix. For all extraction liquids considered, the lowest heavy metal co-extraction was found in SSA samples obtained at 1000 °C (< 21% total heavy metals extracted). However, the incorporation of P into silicate melt agglomerates at that incineration temperature reduced the P extraction. As a result, an incineration temperature in the range 800 – 850 °C offered a good trade-off between high P extraction and low heavy metal co-extraction.

Monitoring of Lithium Contents in Lithium Ores and Concentrate-Assessment Using X-ray Diffraction (XRD)

Lithium plays an increasing role in battery applications, but is also used in ceramics and other chemical applications. Therefore, a higher demand can be expected for the coming years. Lithium occurs in nature mainly in different mineralizations but also in large salt lakes in dry areas. As lithium cannot normally be analyzed using XRF-techniques (XRF = X-ray Fluorescence), the element must be analyzed by time consuming wet chemical treatment techniques. This paper concentrates on XRD techniques for the quantitative analysis of lithium minerals and the resulting recalculation using additional statistical methods of the lithium contents. Many lithium containing ores and concentrates are rather simple in mineralogical composition and are often based on binary mineral assemblages. Using these compositions in binary and ternary mixtures of lithium minerals, such as spodumene, amblygonite, lepidolite, zinnwaldite, petalite and triphylite, a quantification of mineral content can be made. The recalculation of lithium content from quantitative mineralogical analysis leads to a fast and reliable lithium determination in the ores and concentrates. The techniques used for the characterization were quantitative mineralogy by the Rietveld method for determining the quantitative mineral compositions and statistical calculations using additional methods such as partial least square regression (PLSR) and cluster analysis methods to predict additional parameters, like quality, of the samples. The statistical calculations and calibration techniques makes it especially possible to quantify reliable and fast. Samples and concentrates from different lithium deposits and occurrences around the world were used for these investigations. Using the proposed XRD method, detection limits of less than 1% of mineral and, therefore down to 0.1% lithium oxide, can be reached. Case studies from a hard rock lithium deposit will demonstrate the value of mineralogical monitoring during mining and the different processing steps. Additional, more complex considerations for the analysis of lithium samples from salt lake brines are included and will be discussed.

Butt-joint regrowth method by MOCVD for integration of evanescent wave coupled photodetector and multi-quantum well semiconductor optical amplifier

We have realized integration of evanescent wave coupled photodetector (ECPD) and multi-quantum well (MQW) semiconductor optical amplifier (SOA) on MOCVD platform by investigating butt-joint regrowth method of thick InP/InGaAsP waveguides to deep etched SOA mesas. The combination of inductively coupled plasma etching and wet chemical etching technique has been studied to define the final mesa shape before regrowth. By comparing the etching profiles of different non-selective etchants, we have obtained a controllable non-reentrant mesa shape with smooth sidewall by applying one step 2HBr:2H3PO4:K2Cr2O7 wet etching. A high growth temperature of 680 °C is found helpful to enhance planar regrowth. By comparing the growth morphologies and simulating optical transmission along different directions, we determined that waveguides should travel across the regrowth interface along the [110] direction. The relation between growth rate and mask design has been extensively studied and the result can provide an important guidance for future mask design and vertical alignment between the active and passive cores. ECPD-SOA integrated device has been successfully achieved by this method without further regrowth steps and provided a responsivity of 7.8 A/W. The butt-joint interface insertion loss is estimated to be 1.05 dB/interface.

Dual Synthesis of Silver and Iron Oxide Nanoparticles from Edible Green Amaranthus Viridis and their In vitro Antioxidant Activity and Antimicrobial Studies

Background: There is an increasing commercial demand for nanoparticles due to their wide applicability in various areas, such as chemistry, catalysis, energy and medicine. Metallic nanoparticles are traditionally synthesized by wet chemical techniques where the chemicals used are quite often toxic and flammable. Objective: In the present study, we have described a simple, cost-effective and environmentally- friendly technique for green synthesis of silver and iron nanoparticles by using the aqueous extract of leafy vegetable Amaranthus viridis as a reducing agent. Methods: The silver and iron nanoparticles (Av-AgNPs, Av-IONPs) were characterized by different spectral methods. The surface plasmon resonance spectrums of Av-AgNPs, Av-IONPs were recorded at 422nm and 261nm. The scanning electron microscopy (SEM) analysis reveals that the Av-AgNPs and Av-IONPs are roughly spherical in shape. Energy dispersive absorption spectroscopy (EDAX) of biosynthesized Av-AgNPs and Av-IONPs indicates the reduction of silver ions to elemental silver and iron ions to elemental iron. Results: The particle size analysis of Av-AgNPs and Av-IONPs was carried out by the dynamic light scattering (DLS) method; the results reveal both Av-AgNPs and Av-IONPs to be polydispersed in nature. The average particle size of Av-AgNPs is 55.8 nm with a polydispersed index (PI) of 0.297; similarly, the average particle size of Av-IONPs is 80.6 nm with a polydispersed index (PI) of 0.469. Zeta-potential of Av-AgNPs was detected at -24.6 mV and Av-IONPs were detected at 28.8 mV; the result reveals that their high stability may be due their high negative charge and positive charge, respectively. The dual synthesized Av-AgNPs and Av-IONPs exhibited excellent antioxidant activity by DPPH, H2O2 and NO methods. DPPH was proven to be the best when compared with the other two methods. The biosynthesized Av-AgNPs and Av-IONPs proved to have very good antimicrobial activity against gram +ve and gram –ve bacteria. Conclusion: Compared with the standard antibiotic, there are several reports on the green synthesis of metal nanoparticles using various plant parts, but here, edible leafy vegetable Amaranthus viridis was used for biosynthesis of both Av-AgNPs and Av-IONPs.

Ultrasound-assisted wet chemical synthesis of texturized Mo/MoO3 spectrally selective solar absorber coatings

A simple, low-cost Mo/MoO3 textured spectrally selective solar absorber coating prepared using an ultrasound-assisted wet chemical technique on a Mo substrate at different chemical reaction times is presented. The X-ray diffraction structural analysis of the textured coatings revealed only peaks related to Mo from the substrate, implying that the MoO3 coatings were amorphous at ambient temperature. X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy confirmed the presence of Mo+6 ions representing MoO3 in the coatings. The topologic investigations using atomic force microscopy indicated texturized growth with an average surface roughness of 53.15 nm for the sample attacked for 4 h. Absorption bands related to M=O and Mo-O stretching bonds were evident from Fourier transform infrared measurements. Scanning electron microscopy investigations confirmed the presence of surface texturing and agglomerated nanoparticles in the coatings. Optical investigations of the MoO3 coatings on the Mo substrate revealed both a high solar absorptance of 0.91 and a low thermal emittance of 0.05 at 100°C indicating very good solar selectivity. These optical properties can arise from both light trapping which favors multiple absorptions, and intrinsic effects that result from the textured and intrinsic spectrally selective solar absorber design. These results demonstrate that Mo/MoO3 textured and intrinsic coatings deposited by using ultrasound-assisted chemical bath etching and oxidation are exceptional materials for selective solar absorber applications.

Competing Sorption of Se(IV) and Se(VI) on Schwertmannite

Schwertmannite (SHM) is a naturally occurring mineral that has been shown to effectively scavenge oxyanions from contaminated water. In this study, Fourier-transform infrared spectroscopy and X-ray absorption spectroscopy techniques in combination with wet-chemical techniques were used to study the competitive sorption of Se(IV) and Se(VI) at pH 3. The experiments were conducted with three types of schwertmannite obtained from oxidative synthesis, biogenic synthesis and high-pressure compaction at different initial Se concentrations and mixing ratios for 48 h and 56 days, respectively. A threshold value for the uptake mechanisms was identified, which reflects the amount of easily exchangeable sulphate (~0.5 mmol/g). At adsorbate concentrations below this threshold, an inner-sphere corner-sharing bidentate binuclear complex forms upon exchange with sulphate. At higher concentrations, both oxyanions become bound to SHM through co-occurrence of mainly inner-sphere and partly outer-sphere corner-sharing bidentate binuclear complexes with Fe(III) containing surface sites. Single species experiments clearly indicate a higher affinity of SHM for Se(IV). However, in mixed species experiments, competitive sorption occurs with equal or even preferential uptake of Se(VI) at concentrations much lower than the threshold value, presumably due to geometrical similarity between selenate and sulphate, and increasing preference for Se(IV) at high Se concentrations.

Effect of Sb on precipitation of biogenic minerals during the reduction of Sb-bearing ferrihydrites

Antimony (Sb) is a naturally occurring element; it is enriched in the environment by anthropogenic activities. Like other metalloid species, Sb partitions to mineral phases such as oxyhydroxides. In reducing environments, Fe(III) may serve as a terminal electron acceptor during dissimilatory iron reduction leading to its transformation. Relatively little is known concerning the effect of Sb(V) on the precipitation of biogenic minerals in relation to microbiologically mediated redox reactions. To further our understanding, Sb-bearing ferrihydrites (0.5 g) with variable Sb/(Fe + Sb) molar ratios of 0.04, 0.06 and 0.1, were incubated in the presence of Shewanella oneindensis MR-1 (1 × 108 cell mL−1) under N2 atmosphere. Additionally, we synthesized abiotic GR1(CO32−) in the presence of Sb(V) to examine the effect of Sb(V) on this mineral formation and stabilization. A combination of wet chemistry and solid analysis techniques (XRD, Mössbauer and Raman spectroscopies) was used to characterize the reactions.The Sb loading affected the rate and the extent of bio-reduction compared with pure ferrihydrite. Only a minor fraction of the total Sb, less than 0.5%, was released into the solution by the end of the incubation period, suggesting that the metalloid partitioned mainly in a newly formed phase. Furthermore, XPS analyses showed the presence of Sb(V) and Sb(III) species on the biogenic minerals. Magnetite was the main biogenic precipitate (91%) in the absence of Sb(V). Increasing of the molar ratios [Sb/(Fe + Sb)] to 0.1 resulted mainly in the precipitation of carbonated green (47%) rust and goethite (37%). Abiotic green rust synthesis carried out in the presence of Sb(V) indicated the latter’s stabilizing effect on the green rust structure, as for phosphate species. Thus, it is likely that Sb(V) preserve biogenic green rust, hindering its transformation to more thermodynamically stable phases.

Physico-chemical characterization, thermal decomposition and kinetic modeling of Digitaria sanguinalis under nitrogen and air environments

The study undertook the thermal degradation of a tropical grass species, Digitaria sanguinalis, in nitrogen (pyrolysis) and air (combustion) atmospheres through thermogravimetric analysis as well as comparative kinetic investigation. The differential (Friedman) and integral (Flynn-Wall-Ozawa and Straink) isoconversional methods in conjunction with the Coats-Redfern method were utilized. This was to obtain the kinetic parameters and also predict the probable reaction mechanisms involved in the decomposition process. Before the thermal and kinetic investigations, the grass was analyzed for its physical, chemical, and structural properties utilizing diverse wet-chemistry and spectroscopic techniques. This research attempt is part of a larger project designed to investigate a couple of local grass species, which are invasive by nature, as potential energy crops for pyrolytic and combustion applications. The grass had a fixed carbon content of 17.85% and a calorific value of 13.7 MJ kg−1. The fatty acids detected were from C12 (lauric acid) to C24 (lignoceric acid), with the three most abundant being palmitic (94 mg/g extract), linoleic (27 mg/g extract), and oleic (19 mg/g extract) acids. The average residual weight in air (25.3%) was relatively less than in nitrogen (38.7%), affirming the higher rate of reaction in an oxidative process (combustion). The activation energy profiles in both atmospheres were markedly different, as shown by the Flynn-Wall-Ozawa technique for a conversion ratio of 0.1–0.2 (nitrogen, 149 kJ/mol; air, 177 kJ/mol) and 0.65–0.8 (nitrogen, 366 kJ/mol; air, 170 kJ/mol). Of all the models tested, the model-fitting technique indicates that the chemical reaction and diffusional models play predominant roles in the thermal decomposition of the grass under investigation. The thermal degradation of Digitaria sanguinalis proceeded mainly as complex multi-step reaction mechanisms. Aside from the potential suitability of the grass species for bioenergy applications and biofuels production, it also demonstrated huge capability for biochemical extraction. Future work will incorporate the kinetic data for the associated thermochemical processes development, and the design and optimization of reactors/combustors.

Preparation of Efficient Memristive Films (2D materials) for Flexible Devices and Their Electrical Characterisation

2D materials have various properties which make them potential candidates for better applications in electronic, chemical and biosensing devices. It is certain that so much work have previously been done on 2D materials. However, the aim of this study is to fabricate a material with a better quality that could create room for greater opportunities in electronic, chemical and biosensing devices. This fabrication was performed through exfoliation, and wet chemical means or PVD layer deposition technique. Furthermore, the current state of the electronics industry has necessitated the need for a novel and suitable memory for low cost and large scale flexible electronics materials. These materials should be non-volatile and low-power consuming devices because energy is of global concern. The non-volatility nature and the energy consuming ability of the finally fabrication was investigated from the current vs time curve in order to obtain the energy retention time. After the fabrication of the electronics material, various characterisations were performed on the devices; stability and endurance level was tested from the current vs cycle numbers of the curves. The rationale for these experiments is to take advantage of the Van der Waals multilayer force present in-between the layers of the two-dimensional (2D) materials to form a material with a desirable atomic and accurate quality. The outcome shows improve 2D memeristive material required to address most challenges experienced by electronic devices, particularly in the multilayer thin film. The result shows performance improvement of the memristors by raising the switching endurance at an elevated temperature of 300 oC and above. Finally, the mechanical flexibility and stability together with its endurance level were tested.