Green NiO Research Articles

Trachyspermum ammi Mediated Green Synthesis of NiO Nanoparticles: Dual Role in Photocatalytic Degradation and Anti-bacterial Efficacy

ABSTRACT Nowadays, there is a lot of discussion in science about green chemistry of nanomaterials, from synthesis to various environmental applications. Herein, we describe a simple, environmentally friendly, economically feasible, free of additives, phytosynthetic methodology for the synthesis of cubic phased NiO nanoparticles using the seed extract of Trachyspermum ammi (also known as Ajwain), which acts as a capping and reducing agent that helps in reducing nickel sulphate (NiSO4.6 H2O) to NiO via co-precipitation method. Various spectroscopic techniques were involved in investigating the phase, morphology, functional groups, crystallinity, size, elemental confirmation, optical property with band gap of the green synthesised NiO Nanoparticles. Moreover, green NiO nanoparticles displayed excellent degradation efficiency for the reduction of industrial pollutant, Allura red and possible mechanism were also suggested. Nearly 91.73% of the Allura red was degraded using the synthesised NiO nanoparticles within 90 min when exposed to UV-light. Moreover, the used nanoparticles were renewed and again their photocatalytic performance was assessed for three consecutive cycles. In addition to photocatalytic activity, the green NiO nanoparticles revealed the considerable anti-bacterial activity against Staphylococcus aureus and Escherichia coli and the dead percentage was calculated as 92.56% and 94.33% respectively. In this work, green NiO nanoparticles was involved as a dual functioning agent for effective photocatalytic and anti-bacterial studies.

Chitosan-sunflower meal biochar hydrogel incorporated with green synthesized NiO nanoparticles for enhanced catalytic reduction of anthropogenic water pollutants.

Anthropogenic activities have been one of the crucial driving factors for water pollution globally, thereby warranting a sustainable strategy for its redressal. In this study, we have developed a hydrogel-biochar nanocomposite for catalytic reduction of water pollutants. To begin with, green synthesis of nickel oxide nanoparticles (NiO NPs) was accomplished from waste kinnow peel extract via the environmentally benign microwave method. The formation of NiO NPs was affirmed from different analytical techniques namely ultraviolet-visible (UV-Vis), Fourier transform infrared (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy-dispersive spectroscopy (EDS). The FESEM images revealed spherical nature of NiO NPs. The average particle size was found to be 15.61 nm from XRD data. A novel hydrogel-biochar nanocomposite comprising the green NiO NPs, sunflower meal biochar and chitosan was prepared (Cs-biochar@ NiO) and explored as a nanocatalyst towards catalytic reduction of pollutants such as 4-nitrophenol, potassium hexacyanoferrate (III) and organic dyes methyl orange (MO), Congo red (CR), methylene blue (MB) in the presence of a reducing agent, i.e. NaBH4. Under optimized conditions, the reduction reactions were completed by 120 s and 60 s for 4-NP and potassium hexacyanoferrate (III) respectively and the rate constants were estimated to be 0.044 s-1 and 0.110 s-1. The rate of reduction was found to be faster for the dyes and the respective rate constants were 0.213 s-1 for MO, 0.213 s-1 for CR and 0.135 s-1 for MB. The assessment of the nanocatalyst in the reduction of binary dye systems depicted its selectivity towards the anionic dyes CR and MO. The nanocatalyst displayed effective reduction of dyes in real-water samples collected from different sources. Taken altogether, this study validates the design of sustainable hydrogel-biochar nanocatalyst for the efficient reduction of hazardous anthropogenic water pollutants.

Mesoporous NiO/Ni2O3 nanoflowers for favorable visible light photocatalytic degradation of 4-chlorophenol

The present study highlights the treatment of industrial effluent, which is one of the most life-threatening factors. Herein, for the first time, two types of NiO (green and black) photocatalysts were prepared by facile chemical precipitation and thermal decomposition methods separately. The synthesized NiO materials were demonstrated with various instrumental techniques for finding their characteristics. The X-ray diffraction studies (XRD) and X-ray photoelectron spectroscopy (XPS) revealed the presence of Ni2O3 in black NiO material. The transmission electron microscopic (TEM) images engrained the nanospherical shaped green NiO and nanoflower shaped black NiO/Ni2O3 materials. Further, the band gap of black NiO nanoflower was 2.9 eV compared to green NiO having 3.8 eV obtained from UV–vis spectroscopy. Meanwhile, both NiO catalysts were employed for visible light degradation, which yields a 60.3% efficiency of black NiO comparable to a 4.3% efficiency of green NiO within 180 min of exposure. The higher degrading efficiency of black NiO was due to the presence of Ni2O3 and the development of pores, which was evident from the Barrett-Joyner-Halenda (BJH) method. Type IV hysteresis was observed in black NiO nanoflowers with high surface area and pore size measurements. This black NiO/Ni2O3 synthesized from the thermal decomposition method has promoted better photocatalytic degradation of 4-chlorophenol upon exposure to visible light and is applicable for other industrial pollutants.

Marine carrageenan‐based NiO nanocatalyst in solvent‐free synthesis of polyhydroquinoline derivatives

This study presents the preparation of nickel oxide nanoparticles (NiO NPs) in the presence of marine seaweed kappa‐carrageenan (κ‐carrageenan) polysaccharide as a green stabilizer and coating agent under optimal conditions. Thermal gravimetric analyzer (TGA) and Fourier transform infrared (FTIR) results revealed thermal stability and the presence of functional groups of κ‐carrageenan‐coated NiO (NiO@κ‐Car) NPs. The color change of the solution from green to black and advent peak at 320 nm primitively confirmed the formation of NiO NPs. Further, transmission electron microscopy (TEM) images of NiO@κ‐Car demonstrate rather irregular spherical and cubic morphology, showing an average size of 18 ± 1.5 nm. Further, X‐ray diffraction (XRD) analysis confirms that NiO NPs appear as cubic crystal structures with a crystallite size of 23.7 nm. According to the turnover number (TON) and turnover frequency (TOF) results, green NiO@κ‐Car exhibits superior catalytic efficiency in one‐pot multicomponent synthesis of polyhydroquinoline derivatives under free‐solvent conditions. Hydrogen‐1 (1H) and carbon‐13 (13C) nuclear magnetic resonance (NMR) spectra indicated the successful synthesis of various organic products. The key advantages of the proposed efficient synthetic protocol include reusability of the catalyst (four runs), simple workout, high yield of the products, environmental sustainability, and solvent‐free reaction condition. A possible mechanism was also suggested, indicating the role of NiO@κ‐Car as a proficient heterogeneous nanocatalyst in the reaction.

A comparative study of green and chemically synthesized nano nickel oxide for multifunctional applications

Nickel oxide nanoparticles [NiO NPs] were synthesized using chemical (Combustion method) and green route using Coccania grandis leaf extract (Probe sonication method). SEM reveals that, NiONPs synthesized using green route showed agglomerated porous, having diameter of 200 nm. Whereas, chemically synthesized NiO NPs were uniform in size with diameter of 180 nm. From PXRD analysis, average crystallite size of green and chemically synthesized NiONPs was found to be 52.6 nm and 41.9 nm respectively. NiO NPs synthesized using the green route. Antibacterial study of NiONPs (synthesized by green route) displayed maximum zone of inhibition i.e10.8mm (Staphylococcussp), 9.4mm (E coli) and 7.4mm (Pseudomonas) compared to 8mm (Staphylococcussp), 9mm (Ecoli). Photocatalytic activity of direct green dye was effective in NiO NPs synthesized by chemical (69.25%) compared to the green route (25.65%). In electrochemical analysis (biosensor), one reduction and one oxidation peak were observed and were highly effective in sensing Fe3+ under alkaline medium in green route NiO NPs.

Structural, Morphological and Optical Behavior of Green Synthesized NiO Nanoparticle for Methylene Blue Photo-Degradation

Green synthesis methodology was used in this report to prepare the NiO nanoparticle for methylene blue (MB) dye photodegradation reaction. Various analytical performances were used to determine the physiochemical performance of the prepared NiO nanoparticle. The NiO nanoparticle has particle range of 20—30 nm with energy gap of 3.38 eV. The degradation efficiency against MB dye was evaluated and degradation under various environmental conditions were studied. The elemental scavenging test was conducted to understand the possible reaction mechanism for MB degradation reaction. As a result, we believe that this green synthesis NiO can open up new avenues for photocatalytic preparation and environmental remediation.

Green Synthesis of NiO Nanoparticle Using Ziziphus Spina-Christi Leaves Extract for Photocatalytic Methylene Blue Dye Degradation

In this presented work, ziziphus spina-christi leaves extract assisted green synthesise approach was used to prepare the NiO nanoparticle for UV light driven photocatalytic methylene blue (MB) dye degradation. Various analytical characterizations were used to understand the crystalline, structural, optical and morphological nature of the prepared nanoparticle. The prepared NiO nanoparticle have wide bandgap of 3.35 eV with average particle size of around 10–15 nm in range. Various environmental conditions and elemental trapping experiments were conducted to understand the factors affecting the MB degradation and main active species for the redox reaction. Hence, we hope that this green synthesise NiO would pave a new way for photocatalytic preparation and their environmental remediation application.

Gastric bioaccessibility is a conservative measure of nickel bioavailability after oral exposure: Evidence from Ni-contaminated soil, pure Ni substances and Ni alloys.

Oral bioaccessibility (BAc) is a surrogate for the bioavailability (BAv) of a broad range of substances, reflecting the value that the approach offers for assessing oral exposure and risk. BAc is generally considered to have been validated as a proxy for oral BAv for the important soil contaminants Pb, Cd, and As. Here, using literature data for Ni BAc and BAv, we confirmed that Ni BAc (gastric only, with HCl mimicking stomach conditions) is a conservative measure of BAv for the oral exposure pathway. Measured oral BAv of Ni in soil was shown to be 50-100 times less than the simplest oral BAc estimates (%BAv=0.012(%BAc) - 0.023 (r=0.701, 95%CI [0.456, 0.847], n=30)) in rats, demonstrating a significant conservatism for exposure assessment. The relationship between the oral BAv and BAc of nickel sulfate hexahydrate (NSHH) was comparable to that of soil, with measured oral BAv of NSHH (1.94%) being a small fraction of NSHH gastric BAc (91.1%). BAc and BAv reflect the underlying Ni speciation of the sample, with the bioaccessible leaching limits being represented by the highly soluble Ni salts and the poorly soluble Ni monoxide, and the environmental (e.g. soil properties) or gastric (e.g. food present) conditions. BAc has potential utility for chemical classification purposes because pure Ni substances can be grouped by %BAc values(using standardized methodologies for the relevant exposure routes), these groupings reflecting the underlying chemistry and speciation of the samples of substances tested here, with 0.008% %BAc for alloys (SS304, SS316, Inconel, Monel), <1% in green NiO and Ni metal massives, 0.9-23.6% for Ni powders, 9.8-22.7% for Ni sulfides, 26.3-29.6% for black oxidic Ni, and 82-91% for the soluble Ni salts. Oral BAc provides realistic yet conservative estimates of BAv for the hazard classification and risk assessment of Ni substances.

Nickel Oxide-Catalyzed Synthesis of 4-Amino-2H-Chromenes: Its Application in Antimicrobial Studies and Towards Protein Docking

This work involves the synthesis of densely functionalized 2-amino-4H-chromenes by domino Knoevenagel-Michael-cyclization reaction of aromatic aldehydes, β-naphthol and malononitrile in the presence of a catalytic amount of a heterogeneous and reusable green NiO nanoparticle at 50 °C. The biogenic nickel oxide nanoparticles are characterized by Fourier transform infrared radiation, X-ray diffraction analysis, scanning electron microscopy and transmission electron microscopy. The synthesized chromenes are characterized by IR, NMR spectra. The synthesized chromene derivatives are studied for microbial inhibition by Kirby-Bauer disc diffusion method using amikacin and flucanazole as positive control. The compounds are found to have good to moderate antimicrobial activities. Their bio evaluation has been carried out with a protein and identified promising ligands for Mycobacterium tuberculosis InhA through molecular docking.

Effect of non-stoichiometry on the charge storage capacity of NiO conversion anodes in Li-ion batteries

Conversion anodes comprising non-stoichiometric black NiO suffer severe capacity fading in Li-ion batteries despite having a high Li+ ion diffusion coefficient. We attribute this capacity fading to (i) its small crystallite size (~ 8 nm) and (ii) high charge transfer resistance (Rct ~ 60–180 Ω cm2). Small crystallites enhance grain boundaries which promote Li+ ion diffusion without efficient material utilization. In contrast, the stoichiometric green NiO anodes deliver a stable capacity of 280 mAh g−1 over 50 charge-discharge cycles. The comparatively higher capacity of green NiO can be explained from its (i) large crystallite size (~ 104 nm) and (ii) negligible Rct values.

Green synthesis of NiO nanostructured materials using Hydrangea paniculata flower extracts and their efficient application as supercapacitor electrodes

In this report, for the first time, we have applied green synthesis NiO nanoparticles (NiO-NPs) as an electrode material for supercapacitor (SC). Hydrangea paniculata flower extracts were used for the green synthesis of NiO-NPs. The green synthesized NiO-NPs is found to be 33nm with surface area of 78.472m2g−1 along with pore volume and pore size of 0.149cm3g−1 and 4.061nm. The green synthesized NiO-NPs based electrode exhibit high specific capacitance of 752, 709, 644, 603 and 581Fg−1 at current densities of 2.5, 5, 10, 20, and 40Ag−1, respectively, are revealing excellent capacitance retention even at a high current density. More notably, the NiO-NPs electrodes also show outstanding cycling stability up to 5000cycles at 10Ag−1 without discernable capacitance fading. This superior electrochemical performance of NiO-NPs is mainly attributed to the nano-dimention of the particles, which shorten the diffusion path lengths for both ions and electrons, ease migration during the rapid charge-discharge process and consequently improve the effective electrochemical utilization of electroactive material.

Hydrogen Reduction of NiO Particles in a Single-Stage Fluidized-Bed Reactor without Sticking

A commercial NiO (green nickel oxide, 86 wt% Ni) powder was reduced using a batch-type fluidized-bed reactor in a temperature range of 500 to 600 oC and in a residence time range of 5 to 90 min. The reduction rate increased with increases in temperature; however, agglomeration and sintering (sticking) of Ni particles noticeably took place at high temperatures above 600 oC. An increasing tendency toward sticking was also observed at long residence times. In order to reduce the oxygen content in the powder to a level below 1 % without any sticking problems, which can lead to defluidization, proper temperature and residence time for a stable fluidized-bed operation should be established. In this study, these values were found to be 550 oC and 60 min, respectively. Another important condition is the specific gas consumption rate, i.e. the volume amount (Nm3) of hydrogen gas used to reduce 1 ton of Green NiO ore. The optimum gas consumption rate was found to be 5,000 Nm3/ton-NiO for the complete reduction. The Avrami model was applied to this study; experimental data are most closely fitted with an exponent (m) of 0.6 ± 0.01 and with an overall rate constant (k) in the range of 0.35~0.45, depending on the temperature.

Origin of the Black Color of NiO Used as Photocathode in p-Type Dye-Sensitized Solar Cells

We report herein on the origin of the black color of NiO, the widespread p-type semiconductor used as photocathode in p-type dye-sensitized solar cells (DSSCs). Clearly, the presence of nickel metal (Ni0) was revealed by X-ray diffraction analyses and X-ray photoelectron spectroscopy in all NiO samples we have prepared according to chemical routes usually employed for DSSC applications. Thus, the black color of the cathodes is correlated to the existence of Ni0 and not to the increased amount of Ni2+/Ni3+ mixed valence as commonly suggested in the literature. Surprisingly, the presence of elemental nickel does not seem to affect drastically the photovoltaic performances of DSSCs that is rather controlled by the amount of chemisorbed dye. Sintering of NiO samples at higher temperature (i.e., from 450 to 900 °C) triggers the progressive oxidation of Ni0 and ultimately leads to pale green NiO samples, but to larger particles size that results in lower conversion efficiencies.

Insoluble Ni compound-induced gene amplification/gene silencing causes over-expression of microtubules/microfilaments, cell shape changes, and de-regulation of global gene expression/Ca+2 gradients, inducing morphological/ neoplastic transformation of 10T1/2 mouse embryo cells

Inhalation of Ni-containing sulfidic ore dusts and smoking cigarettes in Ni refineries causes human respiratory cancer. Inhalation of Ni3S2 or green NiO induces respiratory cancer in rats. Ni3S2 and green NiO were phagocytosed into and induced morphological/A. I./neoplastic transformation in 10T1/2 mouse embryo cells. mRNA differential display showed that 130 genes were differentially expressed between non-transformed and two MCA/four Ni-transformed, 10T1/2 cell lines. Ni/MCA-transformed cell lines displayed a) ect-2 gene amplification/higher levels of ect-2 mRNA/protein; b) increased levels of calnexin mRNA/protein; and c) absence of DRIP80 and β-centaurin-2 mRNAs. We hypothesized amplification of the ect-2 gene led to higher steady-state levels of rhoA-GTP, inducing higher steady-state levels of microtubules (MTs) in Ni/-MCA transformed cell lines. We stained non-transformed/transformed 10T- 1/2 cell lines with fluorescent antibody to α-tubulin/β-tubulin, to stain MTs. MTs were distributed homogeneously in long, thin fibers in non-transformed 10T1/2 cells, but present at higher levels/aggregated in some areas/missing in other areas of transformed cells, confirming hypothesis #1. We next hypothesized transcriptional silencing of the β-centaurin-2 gene led to increased steady-state levels of microfilaments (MFs) and altered their intracellular distribution, in Ni/MCA transformed cell lines. We stained cells with fluorescent phalloidin, a fungal toxin that binds to MFs, and demonstrated MFs were distributed homogeneously in long, thin fibers in non-transformed 10T1/2 cells, but present at higher levels/aggregated, in some areas and missing in other areas of transformed cells, confirming hypothesis #2. Over-expression/clumping of MFs/MTs rounded transformed cells, altering their contact with extra-cellular matrix. Third, we hypothesized that silencing the DRIP80 gene led to alterations in Ca+2 ion gradients in transformed cell lines, and confirmed this by staining cells with the Ca+2 fluorophore, FLUO 3AM. This would alter activities of Ca+2-dependent enzymes in transformed cell lines, contributing to aberrant physiologies. Ni+2 ion therefore induced ect-2 gene amplification/over-expression and caused silencing of the β-centaurin-2 and DRIP80 genes, leading to over-expression of MTs/ MFs, respectively, hence cell shape changes and altered gene expression, and to aberrant Ca+2 ion gradients, which would cause changes in activities of Ca+2-dependent enzymes. Changes in MTs, MFs, and Ca+2 ion gradients would de-regulate expression of 130 genes/alter Ca+2-dependent enzyme activities, contributing to induction of cell transformation.

Ammonia synthesis at atmospheric pressure using a reactor with thin solid electrolyte BaCe 0.85Y 0.15O 3−α membrane

A thin proton conduction electrolyte BaCe 0.85Y 0.15O 3−α (BCY15) membrane was deposited on a porous green NiO–BCY15 substrate by a modified spin-coating method. The dense, crack-free electrolyte BCY15 layer with thickness of ca. 30 μm was obtained after the bi-layer was co-sintered at 1400 °C for 5 h. With Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3−α as the cathode, a membrane reactor for ammonia synthesis at atmospheric pressure was assembled. The membrane reactor was characterized by field-emission scanning electron microscope (FESEM), X-ray diffraction (XRD) and electrochemical AC impedance. The peak ammonia formation rate of about 4.1 × 10 −9 mol s −1 cm −2 was achieved with an imposed DC current 1 mA at 530 °C. The process based on a further optimized BCY15 membrane reactor may be a potential route for ammonia synthesis at atmospheric pressure.

Synthesis, properties and supramolecular structure of di(aqua)bis(ethylenediamine)nickel(II) bis(4-nitrobenzoate)

The reaction of the sodium salt of 4-nitrobenzoic acid (4-nbaH) with [Ni(H2O)6]Cl2 or [Ni(en)3]Cl2·2H2O (en is ethylenediamine) results in the formation of the known octahedral compound [Ni(H2O)4(η 1-4-nba)2]·2H2O (4-nba = 4-nitrobenzoate) 1 or the title compound di(aqua)bis(ethylenediamine) nickel(II) bis(4-nitrobenzoate) 2 respectively. Compounds 1 and 2 were characterized by elemental analysis, infrared spectra, DSC thermograms, weight loss studies and the structure of 2 was determined. Both 1 and 2 can be thermally decomposed to green NiO. The title compound [Ni(H2O)2(en)2](4-nba)2 2 crystallizes in the centrosymmetric monoclinic space group P2 1 /c with the Ni(II) situated on an inversion center. The crystal structure of 2 consists of a hexacoordinated Ni(II) complex cation and an uncoordinated 4-nba anion. In the octahedral complex cation, the central metal is linked to two symmetry related bidentate en ligands and two water molecules. In the crystal structure, the cations and anions are linked by three varieties of hydrogen bonding interactions. A comparative study of seven nickel 4-nitrobenzoate compounds is described.

Laser drilling of Ni–YSZ cermets

Pulsed Nd:YAG laser was used for efficient drilling of cylindrical hole patterns in porous Ni–YSZ cermet plates. Green NiO–YSZ oxide ceramic substrates obtained via tape casting technique were machined using 8–80 ns pulses at the fixed wavelength of 1064 nm. The etched volume, drill diameter, shape and depth were evaluated as a function of the processing parameters such as pulse irradiance and pulse number. The laser machining mechanism was discussed by means of laser–material interaction parameters such as beam absorptivity and plasma formation and the impact to the overall process discussed. Holes with uniform diameter from 30 to 110 μm and up to 1 mm depth were drilled with a high efficiency of up to 0.1 mm 3 per pulse. Green state machining showed significant efficiency whereas the properties of the cermet substrate were kept unchanged.

Fabrication of ceramic films for solid oxide fuel cells via slurry spin coating technique

Thin ceramic films of samaria-doped ceria (SDC) were deposited on green NiO–SDC substrate via a slurry spin coating technique followed by co-firing. The ceramic films as-prepared are homogenous and dense, without cracks and penetrating pinholes, as observed from cross-sectional SEM images. The thicknesses of the ceramic films for one coating run can be adjusted between 0.8 and 9 μm by altering the spin rate. The film thickness ( h) is inversely proportional to the logarithm of the spin rate (Log( f)) in the range of 3000–10,000 rpm. The slurry spin coating procedure is largely a competition between the thinning and the drying. Half-cells with both 15 and 25 mm diameters were fabricated. In addition, YSZ electrolyte layer with a thickness of 15 μm was also deposited with a homogeneous and completely dense microstructure by two runs of slurry spin coating.

Spectroscopic study of a Ni-bearing gahnite pigment

In the course of the synthesis of a blue Ni-bearing gahnite (ZnAl 2O 4), a green phase was often observed contaminating the blue products of the synthesis, thus affecting the chromatic stability of the material. Both the blue and the green phases were characterised by means of X-ray powder diffraction (XRD) and diffuse reflectance spectroscopy (DRS), in order to understand the nature of the blue colour and of the contamination. For both phases, the Rietveld refinement of the XRD powder patterns indicates that gahnite is indeed the main phase present. The blue product also contains minimal amounts of corundum (Al 2O 3). The colour of the blue phase was related to the tetrahedral crystal field surrounding Ni 2+ in gahnite. Nevertheless, only a small fraction of tetrahedrally coordinated Ni was determined, being this ion mostly distributed over the octahedral sites. The green phase is apparently homogeneous, both under the electron microscope and from interpretation of XRD. However, from the DRS spectrum, it is suggested that the green colour could result from a mixture of the blue Ni-bearing gahnite and a small fraction of yellow–green NiO. Probably because of its low amount and/or poor crystallinity, this latter phase is undetectable by XRD. The nature of the chromatic instability of the final products of the synthesis is, therefore, ascribed to an incomplete Ni incorporation in the spinel structure.

Deposition and Clearance Models of Ni Compounds in the Mouse Lung and Comparisons with the Rat Models

Experimental data from inhalation studies in mice were used to develop mathematical models of deposition, clearance, and retention kinetics in the respiratory tract for inhaled Ni compounds (high temperature (green) NiO,Ni3S2, and NiSO4.6H2O) in the mouse lung. For deposition, a new model was developed using the experimental data on nasal deposition and lung morphometry by Phalen (1991). Three major mechanisms of airway deposition, including impaction, sedimentation, and diffusion, were considered in the deposition model. Because of the differences in physiological and ventilation conditions, it was found that mice have a lower alveolar deposition fraction than rats when exposed to the same Ni compounds. In the development of a clearance model, a single compartment model in the lung was used and a general assumption was made that the clearance of the insoluble and moderately soluble Ni compounds (high temperature (green) NiO and Ni3S2, respectively) depends highly on the volume of retained particles in th...