Precipitation Agent Research Articles

Optimization of ZnO Nanoparticles’ Synthesis via Precipitation Method Applying Taguchi Robust Design

Zinc oxide (ZnO) possesses exceptional potential to be utilized in water and wastewater treatment applications, either as a photocatalyst or in membrane incorporation. In the present study, ZnO nanoparticles were synthesized using the precipitation method. The Taguchi approach with the L32b orthogonal array was utilized in order to optimize the experimental conditions for the synthesis of the nanoparticles and to ensure that relatively smaller-sized particles were obtained. The design was characterized by ten factors, where nine of them possessed four levels, while one had two levels. This study’s design factors were the type of Zn precursor, the concentration of the Zn precursor, the type of precipitating agent, the precipitation agent’s concentration, the type of utilized solvent, the pH value of the solvent, the temperature used during the synthetic procedure, the calcination temperature, the time of stirring during synthesis, as well as the stirring speed. The influences of those factors on the selected response parameters (the average crystallite size, degree of crystallinity, energy band gap (Eg), and photodegradation constant (k)) were then evaluated. XRD analysis and the calculated Eg values indicated that the hexagonal wurtzite structure was the only crystalline phase present in the produced samples. The photocatalytic efficiency of all ZnO nanoparticles was examined in the degradation of rhodamine B under UV light irradiation. The optimal conditions were achieved using zinc acetate dihydrate as the Zn precursor at a concentration equal to 0.3 M, sodium hydroxide as the precipitating agent (1.5 M), methanol as the solvent (the pH value of the solvent was equal to 13), a temperature during the synthetic procedure of 70 °C, 600 °C as calcination temperature, a 90 min stirring time, and 700 rpm as the stirring speed. The optimized ZnO sample was synthesized based on the aforementioned conditions and thoroughly characterized. The acquired results confirmed the prediction of the Taguchi approach, and the most enhanced k-value was observed.

Technical and Economic Comparison between Sodium and Ammonium Agents in the Jarosite Precipitation Process-An Evaluation for Industrial Applications.

Iron content can cause severe challenges through zinc production from zinc sulfide concentrate. The zinc industry extensively uses the jarosite precipitation process (JPP) to precipitate dissolved iron and remove it before transferring the solution to downstream stages. Precipitating agents (PAs) play an essential role in the JPP. However, surprisingly, no study compares the efficiency of various PAs on an industrial scale. As an innovative approach, this investigation compares the technical and economic aspects of using various sodium and ammonium compounds (hydroxides, carbonates, bicarbonates, sulfates, and bisulfates) as typical PAs for the JPP at the Bafgh Zinc Smelting Company (BZSC) plant. Experimental results revealed that ammonium hydroxide, with 90.85% iron removal efficiency, had the highest performance, and sodium bisulfate and ammonium bisulfate had the lowest efficiency (74.54 and 77.13%, respectively). However, since ammonium hydroxide is a corrosive PA, it is not a promising alternative to sodium sulfate (with both economic and safety issues). Based on technical and economic assessments, sodium carbonate (84.31% iron removal efficiency) showed the highest potential for an efficient JPP.

Synthesis of Lithium-Nickel-Cobalt-Manganese-Aluminum Oxide-Based Ni-Rich Lib Cathode through Slug-Flow Manufacturing Platform

Lithium ion batteries (LIBs) with high specific capacity and long cycle life is critically required for high energy applications, such as electric vehicle technology. Owing to the high capacity, various Ni-rich cathodes (with Ni-content ≥ 80 %), including lithium-nickel-cobalt-manganese (NCM), lithium-nickel-cobalt-aluminum (NCA)-based layer oxides are widely explored to fabricate high performance LIBs.1 However, increase in Ni-content in the layered oxides aggravated the issues like, poor rate capability and short cycling performance due to the extensive volume contraction/expansion and the phase change above 4.2 V vs. Li/Li+. One rational strategy to achieve both high capacity and high mechanical stability for the Ni-rich cathodes is optimized doping of Al in the NCM moiety. Presence of Mn and Al in the same structure ensures high mechanical as well as thermal stability of the lithium-nickel-cobalt-manganese-aluminum oxide (NCMA).2 The performance of NCMA largely depends on the atomic percentage of each transition metals in the crystal structure. Hence proper control over the elemental composition and morphology is critically required. Among the various synthesis methods, stirred tank reactor-based co-precipitation synthesis through batch or semi-batch process is commonly used to synthesize phase pure NCMA precursors. However, the stirred tank reactor-dependent synthesis of battery precursors suffers from intrinsic batch-to-batch composition variability, increased agglomeration/breakage of particles and scaling up issues.The main goal of our research is to develop a low-cost scalable manufacturing platform for Ni-rich cathodes.3 Herein, we have utilized three-phase slug-flow reactor to produce NCMA oxalate precursor particles with high phase purity, homogeneity in composition and uniformity in particle size distribution (Figure 1). Here, the growth of precursor particles follows the co-precipitation chemistry and each of the self-circulating slugs works as the milliliter scale reactors, which offers better mixing of various reagents of the reaction mixture.3 The reactor is advantageous in terms of selective feeding of components, spatially uniform reaction conditions with high production rate and good control over the precursor composition and particle size, which further determines the tap density of the final material.4 In this work, NCMA oxalate with the compositional variation of Co= 6 – 10 % are synthesized through slug-flow, followed by high temperature lithiation of the precursor at high temperature of 750 oC in oxygen flow to obtain the final oxide material. The ammonium oxalate was used as the primary precipitation agent and ammonium hydroxide plays the roles of pH-controller as well as works as the chelating agent. The as-synthesized NCMA shows a high specific capacity of ~196 mAh g-1 at 0.1 C. The battery performance of the NCMAs are further analyzed by rate capability and cycling performance profiles. References Muralidharan, E. C. Self, M. Dixit, Z. Du, R. Essehli, R. Amin, J. Nanda, I. Belharouak, Adv. Energy Mater. 2022, 12, 2103050.H. Kim, L. Y. Kuo, P. Kaghazchi, C. S. Yoon, Y. K. Sun, ACS Energy Lett. 2019, 4, 576−582.B. Gupta, M. Jiang, M. Mou, A. Patel, J. H. Mugumya, S. Mallick, H. Lopez, M. p. Paranthaman, 2022 Meet. Abstr., MA2022-02, 25. DOI 10.1149/MA2022-02125.Jiang, Z. Zhu, E. Jimenez, C. D. Papageorgiou, J. Waetzig, A. Hardy, M. Langston, R. D. Braatz, Crys. Growth Des. 2014, 14, 851-860.Mou, A. Patel, S. Mallick, J. Mugumya, M. L. Rasche, M. P. Paranthaman, H. Lopez, G. P. Pandey, R. B. Gupta and M. Jiang, ACS Omega 2022, 7, 46, 42408–42417. Figure 1

Comparison of production of mixed rare earth oxide (Nd/Pr oxide) powders by different precipitation agents from NdFeB magnets’ water leaching

ABSTRACT This research compared the production processes for mixed rare earth oxide (Nd/Pr oxide) powders from a leach solution obtained from acid baking with nitric acid followed by water leaching. Furthermore, the precipitation behaviour of the constituent elements in the leach liquor was examined. Development of economically feasible processes is significant on an industrial scale. In this regard, Nd/Pr oxide powders were recovered from the leach solution by using oxalic acid, ammonium oxalic acid (C2H2O4), sodium hydroxide (NaOH), and ammonium hydrogen carbonate (NH4HCO3) in a comparative manner. Experimental investigations showed behavioural similarities between C2H2O4 and NH4HCO3 precipitation agents; they precipitate rare earth elements (REEs), selectively. However, NaOH was different from them as it precipitates constituent elements in the leach liquor. The cost of C2H2O4 and NH4HCO3 on the industrial scale is higher than NaOH. The resulting flow diagrams of the preparation of Nd/Pr oxide powders were comprehensively compared and optimised to propose more environmentally friendly, economical, and sustainable process.

Highly selective photocatalytic CO 2 reduction to ethylene in pure water by Nb 2O 5 nanoparticles with enriched surface –OH groups under simulated solar illumination

Photocatalytic CO₂ reduction to valuable chemical compounds could be a promising approach for carbon neutral practice. In this work, a simple and robust thermal decomposition process was developed with ammonium carbonate as both the precipitation agent and sacrificial template to produce fine Nb₂O₅ nanoparticles with a rich existence of surface -OH groups. It was found by Density Functional Theory (DFT) calculations and experiments that the rich existence of surface -OH groups enhanced the adsorption of both reactants (CO₂ and H₂O molecules) for the photocatalytic CO₂ reduction on these fine Nb₂O₅ nanoparticles, and a highly selective conversion of CO₂ to a high value chemical compound of ethylene (~ 68 mmol·g^-1·h^-1 with ~ 100% product selectivity) was achieved under simulated solar illumination without the usage of any sacrificial agents or noble metal cocatalysts. This synthesis process may also be readily applied as a surface engineering method to enrich the existence of surface -OH groups on various metal oxide-based photocatalysts for a broad range of technical applications.

High-entropy (CoCrFeMnNi)3O4 catalysts for propane catalytic destruction: Effect of the precipitation agent

Efficient catalytic destruction of light alkane with ultra-stable and highly symmetric structure is still an intractable issue. High entropy oxides (HEOs) with high chemical disorder and lattice distortion and superior stability have shown great potential in heterogeneous thermocatalysis. Herein, spinel-type HEOs are synthesized via a scalable co-precipitation method with different precipitants (NaOH, Na2CO3, and NaHCO3) and firstly adopted in catalytic destruction of propane. Results demonstrate that the HEO-NaOH possesses the best activity, achieving 90% of propane conversion at 325 °C with an apparent activation energy of 56 kJ mol−1. Compared with other two HEOs, the HEO-NaOH has larger quantities of surface oxygen vacancies and easily forms several reactive oxygen species (OOH−, O2−, and OH−, etc.), which significantly contribute to improve the catalytic performance. Moreover, the excellent water resistance of HEOs is verified due to their high conformational entropy and structural stability. Reaction mechanism reveals that OOH− and O2− are the key species in the oxidation of C3H8, which break C-H and C-C bonds in sequence, and are then converted to oxygenated compounds via oxygen oxidation before the final mineralization. The present work provides new insights into the fabrication of efficient catalysts for light alkane destruction as well as other thermocatalytic applications.

Synthesis of Carnation-Like ZnO for Photocatalytic Degradation of Antibiotics, Including Tetracycline Hydrochloride

ZnO has been known to be an excellent photocatalyst and production of suitable morphology by cheap methods to increase catalytic efficiency is important in practical applications. In this study, a fast precipitation method was used to produce the carnation-like morphology to improve the performance of ZnO in the removal of tetracycline hydrochloride (TCH). The precursor of zinc nitrate, precipitation agents of sodium hydroxide, and trisodium were used to control the morphology of ZnO. The characterization of as-prepared material was confirmed by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, diffuse reflectance ultraviolet-visible, and N2 adsorption/desorption isotherms. As a result, the ZnO appeared with a regular and uniform three-dimensional carnation-like morphology and consisted of numerous nanosheets with a thickness of 0.013 μm. The average size of the ZnO flowers was 5 μm. In addition, the plausible formation mechanism of nanoflower with time was proposed. The effects of reaction conditions on the catalytic performance of ZnO were thoroughly examined, and its performance was compared with those of other ZnO forms and other materials. As-prepared ZnO showed to efficiently decompose TCH with the decompose efficiency and rate constant of 89.92% and 0.038 min−1, respectively. Moreover, the •O2− and h+ were key active species in the decomposition of the TCH process.

Influence of Nickel Loading and the Synthesis Method on the Efficiency of Ni/TiO2 Catalysts for Renewable Diesel Production

The efficiency of Ni/TiO2 catalysts for renewable diesel production was evaluated in the present study. Two series of catalysts were synthesized and characterized using various physicochemical techniques (N2 physisorption, XRD, SEM, XPS, H2-TPR, and NH3–TPD). In the first series of catalysts, successive dry impregnations (SDI) were used for depositing 10, 20, 30, 50, and 60 wt.% Ni. The yield towards renewable diesel is maximized over the catalyst with 50 wt.% Ni loading. Selecting this optimum loading, a second series of catalysts were synthesized via three additional preparation methods: wet impregnation (WI) and deposition–precipitation using either ammonia (DP-NH3) or urea (DP-Urea) as the precipitation agent. The catalysts’ efficiency in the production of green diesel is influenced by the preparation method following the order: DP-Urea > DP-NH3 > WI ≈ SDI. The metallic surface area and the balanced acidity mainly determine the performance of the catalysts.

The Effect of Metal Ratio and Precipitation Agent on Highly Active Iron-Manganese Mixed Metal Oxide Catalysts for Propane Total Oxidation

Iron-manganese mixed metal oxide catalysts with a range of Fe:Mn ratios were synthesised by co-precipitation using sodium carbonate and evaluated for total propane oxidation. The Fe0.50Mn0.50Ox catalyst was the most active, and this was due to increased surface area along with the formation of a Mn2O3 phase that was not present in the other catalysts. The effect of the precipitating agent was evaluated with the Fe0.50Mn0.50Ox catalyst, investigating preparation using (NH4)2CO3, K2CO3, NH4OH, KOH, and NaOH. In almost all cases, the activity of propane oxidation was increased compared to the Na2CO3-prepared catalyst, with the hydroxide-precipitated catalysts generally being more active than the carbonates. The NH4OH catalyst was the best performing and this was thought to be due to the formation of a highly active mixed defect spinel structure. Results demonstrate that highly active mixed metal oxide total oxidation catalysts can be prepared using abundant elements, and the choice of precipitating agent is important to maximise the activity.

High specific surface area γ-Al2O3 nanoparticles synthesized by facile and low-cost co-precipitation method

Alumina (Al2O3) nanoparticles (NPs) are particularly adsorbent NPs with a high specific surface area (SSA) that may well be utilized to clean water. In this study, pure γ-alumina NPs are successfully synthesized by the co-precipitation method, and the effect of ammonium bicarbonate concentration on the synthesized NPs is studied to find the optimum concentration to provide the highest capacity of copper ions removal from water. The results declare that spherical alumina NPs with average diameters in the range of 19–23 nm are formed with different concentrations of precipitation agent, and the concentration has no significant effect on the morphology of NPs. Furthermore, the precipitating agent concentration influences the optical characteristics of the produced alumina NPs, and the bandgap energies of the samples vary between 4.24 and 5.05 eV. The most important impact of precipitating agent concentrations reflects in their SSA and capacity for copper ion removal Ultra-high SSA = 317 m2/g, and the highest copper removal at the adsorbate concentration of 184 mg/L is achieved in an alkalis solution followed by a neutral solution. However, admirable copper removal of 98.2% is even achieved in acidic solutions with 0.9 g/L of the alumina NPs synthesized at a given concentration of ammonium bicarbonate, so this sample can be a good candidate for Cu ions removal from acidic wastewater.

Unexpected formation of dichloroacetic and trichloroacetic artefacts in gas chromatograph injector during Cannabidiol analysis

The knowledge about the stability of compounds and possible ways of their transformation in the process of sample preparation for analysis and during analysis itself is very helpful in the assessment of possible errors which can appear when an accurate and precise estimation of compound concentration in tested samples is attempted. The present paper shows that a significant amount of CBD present in the blood/plasma sample analyzed by means of GC transforms in the hot GC injector not only to 9α-hydroxyhexahydrocannabinol, 8-hydroxy-iso-hexahydrocannabinol, Δ9-tetrahydrocannabinol, Δ8-tetrahydrocannabinol, and cannabinol but also to the trichloroacetic esters of Δ9-THC and Δ8-THC and, unexpectedly, to their dichloroacetic esters when trichloroacetic acid is used as protein precipitation agent. The increase of GC injector temperature favors the formation of dichloroacetic esters of Δ9-THC and Δ8-THC in relation to their trichloroacetic ones. The appearance of dichloroacetic esters of Δ9-THC and Δ8-THC among CBD transformation products is probably the result of the thermal decomposition of their trichloroacetic esters. The transformation of trichloroacetic derivatives of organic compounds into their dichloroacetic derivatives in GC injector has not been reported yet. The instability of trichloroacetic derivatives of Δ8-/Δ9-THC during their GC analysis is probably accounts for the lack of their GC-MS spectra in the databases. NMR, GC-MS and LC-MS spectra of the newly discovered derivatives constitute an important element of the work. The obtained results demonstrate why the use of trichloroacetic acid for plasma samples deproteinization should be avoided when CBD and/or THC are determined by GC.

Rapid and Efficient Optimization Method for a Genetic Transformation System of Medicinal Plants Erigeron breviscapus.

Erigeron breviscapus is an important medicinal plant with high medicinal and economic value. It is currently the best natural biological drug for the treatment of obliterative cerebrovascular disease and the sequela of cerebral hemorrhage. Therefore, to solve the contradiction between supply and demand, the study of genetic transformation of E. breviscapus is essential for targeted breeding. However, establishing an efficient genetic transformation system is a lengthy process. In this study, we established a rapid and efficient optimized protocol for genetic transformation of E. breviscapus using the hybrid orthogonal method. The effect of different concentrations of selection pressure (Hygromycin B) on callus induction and the optimal pre-culture time of 7 days were demonstrated. The optimal transformation conditions were as follows: precipitant agents MgCl2 + PEG, target tissue distance 9 cm, helium pressure 650 psi, bombardment once, plasmid DNA concentration 1.0 μg·μL-1, and chamber vacuum pressure 27 mmHg. Integration of the desired genes was verified by amplifying 1.02 kb of htp gene from the T0 transgenic line. Genetic transformation of E. breviscapus was carried out by particle bombardment under the optimized conditions, and a stable transformation efficiency of 36.7% was achieved. This method will also contribute to improving the genetic transformation rate of other medicinal plants.

Effect of Alkali and Membrane Area on the Simultaneous Recovery of Nitrogen and Phosphorous from Digestate by Membrane Technology and Chemical Precipitation

Nutrient recovery from the agri-food sector waste is an increasingly recognized option within the framework of the bioeconomy. Membrane technologies and chemical precipitation are among the best valued options for their economic and practical feasibility. In this study, the combination of gas-permeable membrane (GPM) technology for the recovery of nitrogen (N) and the chemical precipitation for phosphorous (P) recovery from anaerobically digested swine manure is evaluated. This work studies the effect of the membrane area and the addition of alkali on N and P recovery efficiencies. Specifically, two different membrane area ratios (180 and 100 g of N per m2 of membrane) with and without the addition of alkali were studied. High nutrient recovery efficiencies, of 77% for N and 80% for P, were obtained after 10 days of experiment with a ratio of 180 g N per m2 of GPM and the addition of NaOH (1.5 N), along with the precipitant agent (MgCl2) for P precipitation. Hence, a combined configuration was proposed to perform an effective simultaneous recovery of N and P with the minimum amount of membrane needed in a short time.

Coordination‐Precipitation Synthesis of Metal Sulfide with Phase Transformation Enhanced Reactivity against Antibiotic‐Resistant Bacteria

AbstractGiven the challenge of bacterial resistance to antibiotics, there is an urgent need to develop alternative antibacterial agents. While some metal sulfides are promising candidates against bacterial resistance, their fundamental mechanism of action (MoA) remains unclear. Herein, a “coordination‐precipitation” method is developed for the synthesis of a metal sulfide library and the evaluation of antibacterial consistency. Employing ethylenediamine as a coordination agent and thioglycolic acid as a precipitation agent, 12 different metal sulfide nanocrystals following the same procedure are synthesized. Antibacterial assessment reveals that six metal sulfides with bactericidal potency perform a common feature of phase transformation. In particular, in the process of manganese sulfide (MnS) transformation to Mn3O4, a highly reactive complex of high‐valance manganese (Mn3+) and polysulfide (S32−) accompanied by superoxide is sustainably generated, which synergistically induces bacterial death with a hallmark of lipid peroxidation (named liperoptosis) specifically toward Gram‐positive Staphylococcus aureus (S. aureus). In addition, this MoA confers MnS with therapeutic effects superior to vancomycin in a methicillin‐resistant S. aureus‐infected skin wound model. This study reveals the correlation between phase transformation and the antibacterial MoA of metal sulfides and provides a general fundamental to design a non‐antibiotic antibacterial candidate against bacterial resistance.

(Magnetic) Cross-Linked Enzyme Aggregates of Cellulase from T. reesei: A Stable and Efficient Biocatalyst.

Cross-linked enzyme aggregates (CLEAs) represent an effective tool for carrier-free immobilization of enzymes. The present study promotes a successful application of functionalized magnetic nanoparticles (MNPs) for stabilization of cellulase CLEAs. Catalytically active CLEAs and magnetic cross-linked enzyme aggregates (mCLEAs) of cellulase from Trichoderma reesei were prepared using glutaraldehyde (GA) as a cross-linking agent and the catalytic activity and stability of the CLEAs/mCLEAs were investigated. The influence of precipitation agents, cross-linker concentration, concentration of enzyme, addition of bovine serum albumin (BSA), and addition of sodium cyanoborohydride (NaBH3CN) on expressed activity and immobilization yield of CLEAs/mCLEAs was studied. Particularly, reducing the unsaturated Schiff's base to form irreversible linkages is important and improved the activity of CLEAs (86%) and mCLEAs (91%). For increased applicability of CLEAs/mCLEAs, we enhanced the activity and stability at mild biochemical process conditions. The reusability after 10 cycles of both CLEAs and mCLEAs was investigated, which retained 72% and 65% of the initial activity, respectively. The thermal stability of CLEAs and mCLEAs in comparison with the non-immobilized enzyme was obtained at 30 °C (145.65% and 188.7%, respectively) and 50 °C (185.1% and 141.4%, respectively). Kinetic parameters were determined for CLEAs and mCLEAs, and the KM constant was found at 0.055 ± 0.0102 mM and 0.037 ± 0.0012 mM, respectively. The maximum velocity rate (Vmax) was calculated as 1.12 ± 0.0012 µmol/min for CLEA and 1.17 ± 0.0023 µmol/min for mCLEA. Structural characterization was studied using XRD, SEM, and FT-IR. Catalytical properties of immobilized enzyme were improved with the addition of reducent NaBH3CN by enhancing the activity of CLEAs and with addition of functionalized aminosilane MNPs by enhancing the activity of mCLEAs.

Removal of Zinc from Concentrated Galvanic Wastewater by Sodium Trithiocarbonate: Process Optimization and Toxicity Assessment

In the present research, the removal of zinc from concentrated galvanic wastewater (pH 3.1, conductivity 20.31 mS/cm, salinity, 10.16 g/L, Chemical Oxygen Demand (COD) 2900 mg O2/L, Total Organic Carbon (TOC) 985 mg/L, zinc (Zn) 1534 mg/L and ethylenediaminetetraacetic acid (EDTA) 70 mg/L) by combination of lime (Ca(OH)2) and sodium trithiocarbonate (Na2CS3) as precipitation agents is studied. Central Composite Design (CCD) and response surface methodology (RSM) were applied for modelling and optimizing the designed wastewater treatment process. Analysis of Variance (ANOVA) and the experimental verification of the model confirmed the consistency of the experimental and estimated data calculated from the model (R2 = 0.9173, R2adj. = 0.8622). The use of Ca(OH)2 and Na2CS3 in the optimal condition calculated from the model (pH = 10.75 ± 0.10, V Na2CS3 dose 0.043 mL/L and time = 5 min) resulted in a decrease in the concentration of Zn in treated wastewater by 99.99%. Other physicochemical parameters of wastewater also improved. Simultaneously, the application of Ca(OH)2 and Na2CS3 reduced the inhibition of activated sludge dehydrogenase from total inhibition (for raw wastewater) to -70% (for treated wastewater). Under the same conditions the phytotoxicity tests revealed that the seed germination index for the raw and treated wastewater increased from 10% to 50% and from 90% to 100% for white mustard (Sinapis alba) and garden cress (Lepidium sativum L.), respectively. The parameters of root and shoot growth showed a statistically significant improvement. Treated wastewater (1:10) showed a stimulating effect (shoot growth) compared to the control sample (GI = -116.7 and -57.9 for S. alba and L. sativum L., respectively). Thus, the use of Na2CS3 is a viable option for the treatment of concentrated galvanic wastewater containing zinc.

Synthesis and Characterization of Nd2O3 Nanoparticles Using Urea As Precipitation Agent

Nanoparticles (NPs) of neodymium oxide were prepared by homogeneous co-precipitation method using neodymium nitrate and urea as precursors. X-ray diffraction (XRD) patterns have been refined by the Rietveld method and the Fourier-transform infrared spectroscopy (FT-IR) showed that the sample had a bandgap of about 4.59 eV. On the other hand, the photoluminescence (PL) spectrum indicated that the sample had a low concentration of singly ionized oxygen vacancies. The paramagnetic property of the NPs has been also tested by vibrating-sample magnetometer (VSM) measurements.

Nickel phase deposition on V2CTx/V2AlC as catalyst precursors for a dry methane reforming: The effect of the deposition method on the morphology and catalytic activity

Dry reforming of methane (DRM) is a promising alternative technology for the production of syngas with simultaneous utilization of two main greenhouse gases (CH4, CO2). However, DRM technology is still an industrially immature process due to the lack of stable and active catalyst. Therefore, the search for new catalytic materials is of great research interest. Recently, MAX and MXenes materials are increasingly being tested as potential materials for catalytic processes including dry reforming of hydrocarbons. However, transition metal carbides may be deactivated under DRM conditions due to phase transition caused by an oxidation process. The combining of the MAX/MXene materials with nickel phase may be beneficial for to improve catalytic activity and stability. In this view, we report preparation and characterization of nickel-modified V2CTx/V2AlC materials. The Ni–V2CTx/V2AlC catalysts were prepared using HF-etching followed by impregnation/precipitation method. The effect of preparation route on morphology and catalytic activity was investigated. The properties of fresh and spent catalysts were evaluated using XRD, XPS, MP-AES, SEM, BET surface area, H2-TPR, CO2-TPD, TG/DTG and TEM techniques. Catalytic activity was investigated in the DRM process at 800 °C and 1 bar. It was found that the V2CTx/V2AlC- based materials undergo phase transition to vanadium oxide V2O3, vanadium carbide V8C7 and aluminium oxide. The presence of nickel was crucial for the catalyst activity of V2CTx/V2AlC- based catalysis. The catalytic activity was different and related to the preparation procedure resulting in dissimilar nickel-phase morphology and intercalation of sodium ions. It was found that the distribution of nickel phase and presence of alkali ions determined catalysts’ activity and stability. The highest activity and stability in DRM process was observed for Ni–V2CTx/V2AlC_IMP catalysts obtained using only impregnation method without precipitation agents. For the catalysts nickel phase was distributed uniformly forming needle-like structures. The CO2 and CH4 conversions during 20 h-test were in the range of 90–93% and 90-80%, respectively. The molar ration of H2 to CO in outlet stream fluctuated from 1.05 in the first hour of the process to 0.95 after 20 h of the DRM. The activity and stability of Ni–V2CTx/V2AlC_IMP catalyst was higher compared to unmodified V2CTx/V2AlC, unetched V2AlC and Ni–SiO2.

Multivariate methods in modelling the removal of nitrogen and phosphorus in deep-bed two-media down-flow sand filters

Abstract Multiple linear regression (MLR) was applied to study the operation and efficiency of simultaneous denitrification with sodium acetate (NaAc) as a carbon and energy source and the chemical precipitation of phosphate with iron salts in a pilot sand filter. Different loads were simulated with the addition of primary settled wastewater (PW) containing suspended solids (SS) and biological SS from the aeration tank. SS from PW partly passed the filter. Biological SS was caught by the filter. The validation of the model showed that phosphorus concentration and chemical oxygen demand reduction were easier to predict correctly than the time of operation of the filter. The reduction of total phosphorus differed between 0.01 and 0.31 mg P/L, and the nitrate concentration in the filtrate differed between 0 and 5.2 mg N/L when comparing the experimental values with the model. Experiments showed filtrate concentrations of 0–0.12 mg PO4-P/L, 3.0–8.8 mg NO3-N/L, and 1.9–34 mg SS/L. The addition of NaAc gave a small increase in the reduction of PO4-P probably because of the assimilation of PO4-P into the denitrifying sludge. The dosage of Fe gave a small decrease in the reduction of NO3-N probably because of PO4-P limitation for denitrifying bacteria, as Fe acts as a precipitation agent upon PO4-P.

Purification of pectin by ultrafiltration in combination with sodium citrate

Ultrafiltration is an effective method to improve the purity of pectin, but membrane fouling is an urgent problem to overcome. In this work, trisodium citrate, sodium caseinate and calcium caseinate were combined with ultrafiltration to separate and purify pectin extract. The molecular weight cutoff (MWCO) of the ultrafiltration membrane and the sodium citrate concentration were optimized using the color and clarity of the pectin extract as indices, and the influence of sodium citrate on the pectin particle size and zeta potential was further studied. Finally, the pectin extraction yield, some physicochemical indices, including galacturonic acid (Gal A) content, esterification degree, and ash content, and the surface morphology of the pectin particles were measured. The results showed that the ultrafiltration membrane fouling was effectively controlled and that the steady-state flux increased by 2-fold when the pectin extract was treated with a polyether sulfone (PES) UF membrane (100 kDa) in combination with sodium citrate at a concentration of 0.25 mg/ml. The pectin extraction yield increased to 16.4%, and the resulting pectin was a higher-ester refined pectin with a Gal A content of 89.7%, DE content of 77.42%, and ash content of 0.63%. The combination of sodium citrate and ultrafiltration was beneficial not only for improving the permeability and separation performance of the ultrafiltration process but also for providing an example of a monovalent salt as a precipitation agent.