Near-neutral pH Values Research Articles

PH Effects in the Electrochemical Reduction of CO at Cu Electrocatalysts in an MEA Cell Configuration

We explore the impact of pH and buffer on the electrochemical reduction of CO at Cu electrocatalysts in a membrane electrode assembly (MEA) cell. Anolytes included alkaline KOH solution with potassium hydrogen phosphate and potassium dihydrogen phosphate buffers with pH values ranging from 8 to 14. Results show near-neutral pH electrolytes enhance acetate selectivity. Figure 1 shows Faradaic efficiencies to acetate over 85% at a current density of 300 mA/cm². More alkaline electrolytes resulted in increasing HER along with coproduction of ethanol and n-propanol.Previous works have shown that ethylene production is enhanced at near-neutral pH values and other works have demonstrated that acetate is more favored in alkaline conditions, with ketene identified as a key intermediate. This study highlights the role of phosphate buffers in acetate selectivity at near-neutral pH. SEM, XPS, and XRD analyses show morphological and compositional changes in the Cu catalyst under different pH conditions. We propose that the phosphate buffers stabilize acetate precursors.Figure 1: Electrochemical performance measurement at different anolyte pH; Faradaic Efficiency of H2, C2H4, CH4, Ethanol, Acetate, and n-Propanol during CO electroreduction in a zero-gap MEA configuration at 300 mA*cm−2. Figure 1

Aerobic biotransformation of Sargassum fluitans in combination with sheep manure: optimization of control variables

ABSTRACT Sargassum fluitans was composted alongside sheep manure, in a transformative process that significantly enhanced the algal material’s properties. Post the screening/washing/screening pretreatment, the content of total volatile solids escalated to 73.20%, while ash content reduced to 16.45%. Concurrently, lignin values surged to 30.12% as the biodegradability factor declined to 21%. The pretreatment decreased electrical conductivity from 11.60 to 1.32 DS/m. Employing a central composite design and response surface analysis pinpointed the optimal substrate combinations for carbon/nitrogen ratios of 35:1 and 25:1. The chosen combinations presented a high coefficient of determination (R2 = 0.9589, carbon/nitrogen ratio; R2 = 0.6584, pH), indicative of a robust statistical fit. Over a 45-day period, composting was conducted using bioreactors or biopiles, maintaining near-neutral pH values and temperatures slightly above ambient levels. The composting process reduced up to 94% of fecal coliforms in the 1:1 combination. Physicochemical analyses confirmed that the final product is a valuable compost-soil improver, with great potential for usage in organic agriculture, reforestation, and urban green spaces. Hence, this research underscores composting as an efficient technique in managing organic waste, including the emergent and seasonal Sargassum fluitans, thus addressing a pressing environmental concern with an innovative, effective solution.

L-Lactic Acid Production via Sustainable Neutralizer-Free Route by Engineering Acid-Tolerant Yeast Pichia kudriavzevii.

l-Lactic acid (l-LA) is a platform chemical obtained via microbial fermentation at a near-neutral pH value. Large amounts of neutralizers are required during this process, which increases the production costs in downstream processing as well as environmental burden. To address this challenge, an acid-tolerant yeast Pichia kudriavzevii E1 was isolated and metabolically engineered to produce l-LA without neutralizers. The genome of strain E1 was sequenced and a CRISPR-Cas9 system was developed in this newly isolated strain. Subsequently, the gene encoding pyruvate decarboxylase (pdc) was knocked out to subdue ethanol formation. Furthermore, the l-lactate dehydrogenase gene from Weizmannia coagulans 2-6 and the codon-optimized L-ldhA gene from Bos taurus were introduced into P. kudriavzevii E1 chromosome to redirect the ethanol fermentation pathway to l-LA production. Deletion of the dld(chr3) gene further increased the optical purity of l-LA. After optimizing fermentation conditions, the maximum titer of l-LA in the 5 L fermenter reached 74.57 g/L without any neutralizers, with an optical purity of 100% and a maximum yield of 0.93 g/g glucose. This is the first report of optically pure l-LA production without neutralizers and the engineered acid-tolerant yeast paves the way for the sustainable production of l-LA via a green route.

Oxygen Reduction Reaction Activity in Non-Precious Single-Atom (M-N/C) Catalysts-Contribution of Metal and Carbon/Nitrogen Framework-Based Sites.

We examine the performance of a number of single-atom M-N/C electrocatalysts with a common structure in order to deconvolute the activity of the framework N/C support from the metal M-N4 sites in M-N/Cs. The formation of the N/C framework with coordinating nitrogen sites is performed using zinc as a templating agent. After the formation of the electrically conducting carbon-nitrogen metal-coordinating network, we (trans)metalate with different metals producing a range of different catalysts (Fe-N/C, Co-N/C, Ni-N/C, Sn-N/C, Sb-N/C, and Bi-N/C) without the formation of any metal particles. In these materials, the structure of the carbon/nitrogen framework remains unchanged-only the coordinated metal is substituted. We assess the performance of the subsequent catalysts in acid, near-neutral, and alkaline environments toward the oxygen reduction reaction (ORR) and ascribe and quantify the performance to a combination of metal site activity and activity of the carbon/nitrogen framework. The ORR activity of the carbon/nitrogen framework is about 1000-fold higher in alkaline than it is in acid, suggesting a change in mechanism. At 0.80 VRHE, only Fe and Co contribute ORR activity significantly beyond that provided by the carbon/nitrogen framework at all pH values studied. In acid and near-neutral pH values (pH 0.3 and 5.2, respectively), Fe shows a 30-fold improvement and Co shows a 5-fold improvement, whereas in alkaline pH (pH 13), both Fe and Co show a 7-fold improvement beyond the baseline framework activity. The site density of the single metal atom sites is estimated using the nitrite adsorption and stripping method. This method allows us to deconvolute the framework sites and metal-based active sites. The framework site density of catalysts is estimated as 7.8 × 1018 sites g-1. The metal M-N4 site densities in Fe-N/C and Co-N/C are 9.4 × 1018 sites-1 and 4.8 × 1018 sites g-1, respectively.

Degradation of cyanobacterial neurotoxin β-N-methylamino-L-alanine (BMAA) using ozone process: influencing factors and mechanism.

β-N-methylamino-L-alanine (BMAA), which has been considered as an environmental factor that caused amyotrophic lateral sclerosis/parkinsonism-dementia complex (ALS/PDC) or Alzheimer's disease, could be produced by a variety of genera cyanobacteria. BMAA is widely present in water sources contaminated by cyanobacteria and may threaten human health through drinking water. Although oxidants commonly used in drinking water plants such as chlorine, ozone, hydrogen peroxide, and hydroxyl radicals have been shown to effectively degrade BMAA, there are limited studies on the mechanism of BMAA degradation by different oxidants, especially ozone. This work systematically explored the effectiveness of BMAA ozonation degradation, investigated the effect of the operating parameters on the effectiveness of degradation, and speculated on the pathways of BMAA decomposition. The results showed that BMAA could be quickly eliminated by ozone, and the removal rates of BMAA were nearly 100% in pure water, but the removal rates were reduced in actual water. BMAA was primarily degraded by direct oxidation of ozone molecules in acidic and near-neutral conditions, and indirect oxidation of •OH accounted for the main part under strong alkaline conditions. The pH value had a significant effect on the decomposition of BMAA, and the degradation rate of BMAA was fastest at near-neutral pH value. The degradation rates of TOC were significantly lower than that of BMAA, indicating that by-products were generated during the degradation process. Three by-products ([M-H]+ = 105, 90, and 88) were identified by UPLC-MS/MS, and the degradation pathways of BMAA were proposed. The production of by-products was attributed to the fracture of the C-N bonds. This work is helpful for the in-depth understanding on the mechanism and demonstration of the feasibility of the oxidation of BMAA by the ozone process. HIGHLIGHTS: • The reaction of ozonation BMAA was easy to occur. • The degradation rate was fast under near-neutral conditions. • Direct oxidation under neural conditions was the main pathway for ozone degradation of BMAA. • Three products were detected, and the reaction path was inferred.

Hydrothermal Synthesis of Siderite and Application as Catalyst in the Electro-Fenton Oxidation of p-Benzoquinone.

A weak aspect of the electro-Fenton (EF) oxidation of contaminants is the dependence of the Fenton reaction on acidic pH values. Therefore, the rationale of this work was to develop a novel catalyst capable of promoting the EF oxidation process at near-neutral and basic pH values. In this framework, rhombohedral FeCO3 was synthesized hydrothermally and used as a catalyst in the EF oxidation of p-benzoquinone (BQ). The catalyst was characterized using various surface and spectroscopic methods. Moreover, the effects of applied current (100-500 mA), time (1-9 h), catalyst dosage (0.25-1.00 g L-1), and initial concentration of BQ (0.50-1.00 mM) on the total organic carbon removal efficiency were determined. The results indicated that a 400 mA current was sufficient for a 95% total organic carbon removal and that the increase in catalyst dosage had a positive effect on the mineralization of BQ. It was determined that at pH 3, FeCO3 behaved like a homogeneous catalyst by releasing Fe3+ ions; whereas, at the pH range of 5-7, it shifted to a homogeneous/heterogeneous catalyst. At pH 9, it worked solely as a heterogeneous catalyst due to the decrease of Fe ions passing into the solution. Finally, the spent catalyst did not undergo structural deformations after the EF treatment at higher pH values and could be regenerated and used several times.

Designing robust xylan/chitosan composite shells around drug-loaded MSNs: Stability in upper GIT and degradation in the colon microbiota

Long residence times, near-neutral pH values, and release triggered by the enzymatic action of the resident microbiota offer unique opportunities for improved drug delivery in the colon. The fact that a delivery agent must also pass through the complete GI tract without degradation presents a challenge due to widely changing pH conditions. In this study, a promising colon-targeted drug delivery system was composed of a xylan/chitosan composite shell formed on curcumin-loaded mesoporous silica nanoparticles (MSNs). A novel synthesis approach was employed to facilitate precipitation of negatively charged xylan on negatively charged MSNs by concurrent chitosan polymerization. Curcumin-loaded xylan/chitosan-coated MSNs (C-MSNs) were determined to contain nearly 42% xylan by the inclusion of chitosan in a one-to-one ratio with xylan. The xylan/chitosan composite shell demonstrated excellent stability in the acidic upper GI tract. The hydrolysis of glycosidic bonds by resident microbiota was the triggering mechanism for xylan degradation and curcumin release in the colon. The presence of xylan has the further benefit of increasing the number of beneficial bacteria and improving short-chain fatty acid production for improved colon health.

Elimination of contaminants of emerging concern and their environmental risk in world-real municipal wastewaters by electrochemical advanced oxidation processes

In this study, sixteen contaminants of emerging concern (CECs), present in the effluent of the wastewater treatment plant (WWTP) “Salitre” (Bogotá – Colombia), were subjected to several electrochemical advanced oxidation processes (EAOPs). Thus, the elimination of the pharmaceuticals diclofenac, carbamazepine, venlafaxine, Irbesartan, losartan, metronidazole, sulfamethoxazole, trimethoprim, clindamycin, norfloxacin, ciprofloxacin, clarithromycin, erythromycin, and azithromycin, the illicit drug cocaine, and its major metabolite benzoylecgonine was assessed by electro-Fenton (EF), photo-electro-Fenton (PEF), and photo-electro-Fenton in the presence of added oxalic acid (PEFox). A boron-doped diamond and a gas diffusion electrode were used as anode and cathode. After 1 h of treatment, the total concentration of CECs decreased by 36% when PEFox was applied. In the case of EF and PEF, the degradation percentages were lower (29% and 19%, respectively). The highest degradation by using PEFox was due to the enhanced availability of soluble iron ions by forming Fe(III)-oxalate complexes at near-neutral pH values. This allows the Fenton reaction to yield additional HO• radicals. Finally, the effect of EAOPs to reduce the environmental risk associated with the CECs in the WWTP was evaluated. The best system, PEFox, lowered by more than ten times the environmental hazard of the tested CECs in the effluent. This work shows the high potential of PEFox, as tertiary treatment, to eliminate emerging pollutants and reduce their risk in effluents from WWTP. In this system, the added oxalic acid, which has a biodegradable character, could be eliminated in a subsequent biological step.

Characterization of Magnesium Potassium Phosphate Cement-Based Grouting Material Blended with High Volume Industrial Wastes

In the present research, industrial wastes, e.g., fly ash (FA), lithium slag (LS), ground granulated blast furnace slag (GGBS), and red mud (RM) were utilized to prepare the magnesium phosphate cement (MPC)-based grouting material by a two-component grouting method. Successive additions of GGBS within 40% (C1–C5) led to reduced fluidity, increased pH value, and shortened setting time. The compressive strength increased first and then decreased. The strength value reached the maximum at a 20% dosage (C3). Increasing the content of RM from 0% (C4) to 25% (C9) resulted in prolonged setting time and an increased pH value. The fluidity and compressive strength increased first and then decreased. The fluidity and strength value became the highest at a 15% additive ratio (C7). GGBS can significantly improve the strength and water resistance at 7 days and 28 days by the potential hydraulic property. RM has a smaller particle size than MP, making the microstructure denser by the pore-filling effect. Thus, the drying shrinkage was increased after adding GGBS, while it was decreased when incorporating RM. The MPC-based grouting material has a controllable short setting of 3–21 min, self-leveling fluidity above 200 mm, a near-neutral pH value, high early strength (1 day compressive strength of 5 MPa), minor drying shrinkage (one-tenth of OPC), and excellent water resistance (over 85%), which is much superior to traditional grouting materials.

The influence of pH on UV/Vis spectra of gallic and ellagic acid: A combined experimental and computational study

The pH dependence of the UV/Vis spectrum of gallic and ellagic acid was measured in a buffer-free solution to obtain reliable data at wavelengths bellow 230 nm. UV/Vis absorption spectra were also calculated for all possible ionised species of gallic and ellagic acid using time dependent density functional theory (TD-DFT). From pKa values of gallic and ellagic acid the molar fraction of different ionised species was calculated for each pH value. Finally, the simulated spectra at different pH values were obtained as a weighted average of spectra of neutral, once, twice, three-times, and four-times deprotonated species. The calculated spectra were then compared to the experimental spectra, and the peaks in the experimental spectrum were explained in the terms of main electronic transitions that results in the observed absorption bands. At low pH values the agreement between the experimental and calculated spectra was excellent. At near-neutral pH values the majority of the experimental spectra features were well reproduced in the calculated spectra. A satisfactory agreement between experimental and calculated spectrum at high pH values was also achieved by incorporating the calculated spectra of the oxidised species of gallic acid as well as ellagic acid spectra with one lactone ring open.

Cutin:xyloglucan transacylase (CXT) activity covalently links cutin to a plant cell-wall polysaccharide

The shoot epidermal cell wall in land-plants is associated with a polyester, cutin, which controls water loss and possibly organ expansion. Covalent bonds between cutin and its neighbouring cell-wall polysaccharides have long been proposed. However, the lack of biochemical evidence makes cutin–polysaccharide linkages largely conjectural. Here we optimised a portfolio of radiochemical assays to look for cutin–polysaccharide ester bonds in the epidermis of pea epicotyls, ice-plant leaves and tomato fruits, based on the hypothesis that a transacylase remodels cutin in a similar fashion to cutin synthase and cutin:cutin transacylase activities. Through in-situ enzyme assays and chemical degradations coupled with chromatographic analysis of the 3H-labelled products, we observed that among several wall-related oligosaccharides tested, only a xyloglucan oligosaccharide ([3H]XXXGol) could acquire ester-bonds from endogenous cutin, suggesting a cutin:xyloglucan transacylase (CXT). CXT activity was heat-labile, time-dependent, and maximal at near-neutral pH values. In-situ CXT activity peaked in nearly fully expanded tomato fruits and ice-plant leaves. CXT activity positively correlated with organ growth rate, suggesting that it contributes to epidermal integrity during rapid expansion. This study uncovers hitherto unappreciated re-structuring processes in the plant epidermis and provides a step towards the identification of CXT and its engineering for biotechnological applications.

Reconstruction of the glutamate decarboxylase system in Lactococcus lactis for biosynthesis of food-grade γ-aminobutyric acid.

Gamma-aminobutyric acid (GABA), an important bioactive compound, is synthesized through the decarboxylation of L-glutamate (L-Glu) by glutamate decarboxylase (GAD). The use of lactic acid bacteria (LAB) as catalysts opens interesting avenues for the biosynthesis of food-grade GABA. However, a key obstacle involved in the improvement of GABA production is how to resolve the discrepancy of optimal pH between the intracellular GAD activity and cell growth. In this work, a potential GAD candidate (LpGadB) from Lactobacillus plantarum was heterologously expressed in Escherichia coli. Recombinant LpGadB existed as a homodimer under the native conditions with a molecular mass of 109.6 kDa and exhibited maximal activity at 40°C and pH 5.0. The Km value and catalytic efficiency (kcat/Km) of LpGadB for L-Glu was 21.33 mM and 1.19 mM-1s-1, respectively, with the specific activity of 26.67 μM/min/mg protein. Subsequently, four C-terminally truncated LpGadB mutants (GadBΔC10, GadBΔC11, GadBΔC12, GadBΔC13) were constructed based on homology modeling. Among them, the mutant GadBΔC11 with highest catalytic activity at near-neutral pH values was selected. In further, the GadBΔC11 and Glu/GABA antiporter (GadC) of Lactococcus lactis were co-overexpressed in the host L. lactis NZ3900. Finally, after 48 h of batch fermentation, the engineered strain L. lactis NZ3900/pNZ8149-gadBΔC11C yielded GABA concentration up to 33.52 g/L by applying a two-stage pH control strategy. Remarkably, this is the highest yield obtained to date for GABA from fermentation with L. lactis as a microbial cell factory.Key points• The GadB from L. plantarum was heterologously expressed in E. coli and biochemically characterized.• Deletion of the C-plug in GadB shifted its pH-dependent activity toward a higher pH.• Reconstructing the GAD system of L. lactis is an effective approach for improving its GABA production.

Solubilization and separation of o-toluidine and tricyclazole in sodium dodecyl sulfate micelles in micellar enhanced ultrafiltration.

The solubilization laws of pollutants in micelles and their separation efficiency are very important in the successfully efficient application of micellar enhanced ultrafiltration (MEUF). The solubilization behavior of o-toluidine (OT) and tricyclazole (TC) into sodium dodecyl sulfate (SDS) micelles in MEUF was studied using nonlinear equation sets for concentration analysis, which resolved the issue on the overlap of absorption spectra of multicomponent compounds restricting the application of conventional ultraviolet (UV) spectroscopic method. The solubilization isotherms for both pollutants could be best explained by the Langmuir-Freudlich model (R2>0.99) followed by the modes of Langmuir and Freudlich, inferring the complexity of solubilization mechanism and solubilization advantage of monolayer over multilayer. The calculated thermodynamic parameters (ΔG0, ΔH0 and ΔS0) indicated that this process was endothermic and spontaneous. The solubilization of OT and TC well followed the pseudo second-order and pseudo first-order kinetics, respectively. The separation and recovery of SDS solubilizing these two pollutants were also investigated through lowering solution temperature to 2 °C followed by centrifugation. The best recovery rate of about 66% for SDS was achieved containing 10 and 5% of each initial amount of OT and TC, respectively, at near-neutral solution pH value. The recovery of SDS could decrease to some extent under alkaline and acidic conditions.

Enhanced biotreatability of petroleum hydrocarbon-contaminated mining waste coupled with the attenuation of acid drainage production.

A biostimulation study was conducted on mining waste residue with nutrient (nitrogen and phosphorus) and/or liming agent (ash or CaCO3 ) amendment to assess petroleum hydrocarbon (PHC) biodegradation efficiency by indigenous microorganisms. Compounds accumulated and/or released by treated samples were also monitored to determine the potential for acid mine drainage production during biostimulation. The potential for natural attenuation (i.e., the biodegradation of PHC contamination) was initially low but increased significantly upon nutrient addition. The best results were obtained when nutrient addition was coupled with the addition of a liming agent, notably CaCO3 , which contributed to maintaining near-neutral pH values. In fact, during treatment without a liming agent, pH decreased due to the oxidation of sulfide minerals, resulting in acid mine drainage production with increased metals released into sample leachates. Sulfur- and iron-oxidizing bacteria were detected primarily in samples not amended with liming agents, and the predominant organisms were affiliated with Acidithiobacillus spp. and Acidiphilium spp. Overall, the results of the present study demonstrated that amendment with a liming agent when treating PHC-contaminated mining waste residue contributes to maintaining a pH close to neutrality, mitigates sulfate release, and reduces the release of metals without negatively affecting the activity of PHC degraders.

Community Organization and Metagenomics of Bacterial Assemblages Across Local Scale pH Gradients in Northern Forest Soils.

Soil pH has shown to predict bacterial diversity, but mechanisms are still poorly understood. To investigate how bacteria distribute themselves as a function of soil pH, we assessed community composition, diversity, assembly, and gene abundance across local (ca. 1 km) scale gradients in soil pH from ~ 3.8 to 6.5 created by differences in soil parent material in three northern forests. Plant species were the same on all sites, with no evidence of agriculture in the past. Concentrations of extractable calcium, iron, and phosphorus also varied significantly across the pH gradients. Among taxa, Alphaproteobacteria and Acidobacteria were more common in soils with acidic pH values. Overall richness and diversity of OTUs peaked at intermediate pH values. Variations in OTU richness and diversity also had a quadratic fit with concentrations of extractable calcium and phosphorus. Community assembly was via homogeneous deterministic processes in soils with acidic pH values, whereas stochastic processes dominated in soils with near-neutral pH values. Although we expected selection via genes for acid tolerance response in acidic soils, genes for genetic information processing were more selective. Taxa in higher pH soils had differential abundance of transporter genes, suggesting adaptation to acquire metabolic substrates from soils. Soil bacterial communities in northern forest soils are incredibly diverse, and we still have much to learn about how soil pH and co-varying soil parameters directly drive gene selection in this critical component of ecosystem structure.

Use of Zinc Carbonate Spiking to Obtain Phytotoxicity Thresholds Comparable to Those in Field-Collected Soils.

Several studies have reported the presence of smithsonite (ZnCO3 ) in soils polluted by zinc mining. The present study aimed to determine upper critical threshold values of Zn phytotoxicity in a substrate spiked with ZnCO3 and to compare them with those obtained in field-collected soils. We studied Zn toxicity to perennial ryegrass (Lolium perenne L.) grown in pots with unpolluted peat treated with increasing concentrations of ZnCO3 that produced nominal total Zn concentrations of 0, 0.7, 1.3, 2.0, 2.6, and 3.3%. To keep constant near-neutral pH value in all the treatments, we used decreasing concentrations of dolomitic lime. In the treatment with total soil Zn of 3.3% (pH 6.8), the foliar Zn concentration of L. perenne was 1914 ± 211 mg kg-1 , falling into the range of 2400 ± 300 mg kg-1 reported for Lolium species grown under similar laboratory conditions in a polluted soil (total soil Zn 5.4%, pH 7.3) collected near a Zn smelter. The value of 92 ± 98 mg kg-1 was obtained for the median effective concentration (EC50) values of 0.01 M KNO3 -extractable Zn using the responses of shoot dry biomass, shoot length, and total pigments. This value falls within the range of 95 ± 46 mg kg-1 reported in other studies for the EC50 values of salt-extractable Zn using field-collected soils. The application of ZnCO3 for spiking was able to mimic foliar Zn concentrations of Lolium species observed in field-collected soils. The effective concentrations of soil Zn obtained in the present study are comparable to those obtained in field-collected soils. Future research should determine effective concentrations of metals using soils spiked with metal-containing compounds that mimic a real source of contamination. Environ Toxicol Chem 2020;39:1790-1796. © 2020 SETAC.

Kinetic Testing for Oxidation Acceleration and Passivation of Sulfides in Waste Rock Piles to Reduce Contaminated Neutral Drainage Generation Potential

Contaminated neutral drainage (CND), generated when metals are leached and enough neutralizing minerals are present to keep a near-neutral pH, is a growing environmental concern related to mine waste management. There is a need to find ways to reduce CND generation from mine waste to avoid perpetual effluent treatment. Nickel concentrations at the Lac Tio mine effluent have been sporadically higher than provincial environmental standards. In this project, three different treatment solutions were applied to Lac Tio mine waste rock samples in 70 kg waste rock columns in an attempt to reduce nickel CND generation potential by forcing sulfide oxidation and/or passivation. Following the applications, kinetic tests were used to determine any reduction in sulfide oxidation and nickel leaching. Hydrogen peroxide and sodium silicate were the main products tested, alone and in combination with a sodium bicarbonate buffer. Buffered hydrogen peroxide showed the best potential to reduce CND generation, with nickel release reduced from 1.4 × 10–3 mg/kg/day (untreated) to 4.0 × 10–5 mg/kg/day (treated) and near-neutral pH values. This passivation treatment also reduced the sulfur release rate by more than 50%. Optical and scanning electron microscopy observations supported the laboratory results. To conclude, this research project proposes a new way to reduce the CND generation potential of low sulfide waste rock.

Sugarcane bagasse amendment improves the quality of green waste vermicompost and the growth of Eisenia fetida

Vermicomposting is a feasible method for disposing of lignocellulosic waste while generating a useful product. The current study assessed the potential of vermicomposting green waste mixed with sugarcane bagasse in proportions of 25%, 50%, and 75% (v:v, based on dry weight). The suitability was evaluated based on the agrochemical properties, earthworm biomass, and phytotoxicity. The final vermicomposts exhibited near-neutral pH values (7.1–7.6), and lower EC values (0.43–0.72 mS/cm) and C:N ratios (14.1–19.9).The content of available nutrients and CEC for all the vermicomposts exceeded those of the control compost (without earthworms). For vermicomposts, the average values of NO3−-N, AP, AK, and CEC were 53, 517, 1362 mg/kg, and 158 cmol/kg, respectively. The total contents of heavy metals increased in all vermicompost treatments compared to control composts with the following average final percentages: Zn (2.0%), Cr (15.5%), Pb (23.4%), and Cu (44.3%), but these amounts were safe for application in agroforestry. The addition of sugarcane bagasse to green waste significantly increased the content of total humic substance, humic acid and urease activity, acid and alkaline phosphatase activity, and Eisenia fetida reproduction. The addition of 25% sugarcane bagasse to green waste decreased the toxicity to germinating seeds. These results revealed that vermicomposting is a feasible way to degrade green waste into a value-added chemical product.

A versatile and robust surface-poison-resisting Scanning Amperometric Proton Microscopy

Abstract A sensitive and accurate measurement of localized pH with improving spatial resolution is highly desirable to the scientific understanding of many processes ranging from clean energy production to biological cellular mechanisms. In this study, we report the observation that the diffusion-limited current (DLC) of hydrogen evolution reaction (HER) on Pt surface is largely surface poison-resisting to carbon monoxide and thiol, two well-known Pt surface poisons. Building upon this observation, we proposed and tested a technique for amperometrically measuring localized proton concentration with a sub-μm spatial resolution through the utilization of a linear pH dependence of HER DLC on a Pt ultramicroelectrode, hereby referred to as Scanning Amperometric Proton Microscopy (SAPM). By bringing the Pt ultramicroelectrode close to a proton generating/consuming substrate through resonance feedback on an atomic force microscopy (AFM) tuning fork, SAPM can be used to measure and image localized proton concentrations and changes in pH caused by an active catalytic surface during reactions, largely free of concerns about the presence of surface-poisoning species. This was demonstrated through three proof-of-concept cases: methanol oxidation reaction (MOR) on a Pt thin film substrate, active proton-coupled electron transfer by a membrane-tethered protein (cytochrome c oxidase) in biological compatible electrolyte, and SAPM imaging of PtRu islands electrodeposited onto a Pt film substrate during MOR. The development of this surface-poison-resisting scanning probe technique through this study shows the potential of a broadly applicable way to study proton-generating or -consuming reactions for catalytically-active substrates with a sub-μm spatial resolution, including biological processes involving localized pH changes in a variety of salts, buffers or broth-type reaction media at near-neutral pH values.

Synergetic Effect of 1,2,4-triazole and Glycine on Chemical Mechanical Planarization of Aluminum at Low Polishing Pressure in an Eco-Friendly Slurry

In this paper, glycine and 1,2,4-triazole (TAZ) are used as eco-friendly additives to compensate the decrease in removal rate owing to the low polishing pressure in chemical mechanical planarization (CMP) of aluminum (Al) at near-neutral pH value. It demonstrated that the synergetic effect of glycine and TAZ participates in the formation of a weak passive layer with the hardness of 0.419 GPa on Al surface, which is compact enough to protect the Al surface from chemical dissolution and meanwhile relatively weak enough to achieve high polishing rate. Even at a low polishing pressure of 1.0 psi, a material removal rate of 750 nm min−1 with surface roughness of 0.19 nm was obtained in an eco-friendly slurry at pH 7.5. It was found that the weak passive layer is physicochemical formed on surface of Al with Al-TAZ bonds, which is subsequently complexed by glycine with Al-COOH bonds verified by Langmuir isotherm theory and X-ray photoelectron spectroscopy test. The above two synergistic parts are integrated into the material removal process. The material planarization mechanism in CMP process of Al was discussed as well.