High pH Solutions Research Articles

Chemiresistive room temperature H2S sensor based on CunO nanoflowers fabricated by laser ablation

Hierarchical CunO nanoflowers were synthesized through the laser ablation of a CuO target in NaOH solutions for room-temperature (27 ℃) H2S detection. Notably, the pH value of NaOH solutions influenced both the micro-morphologies and compositions of the CunO products, as evidenced by XRD, XPS, SEM and TEM. In high pH solutions, the specific surface area of the CunO products increased, their thickness decreased, and the Cu2O content diminished, resulting in enhanced sensitivity, selectivity and stability of the CunO products’ response to H2S. Notably, the pH14# sample synthesized using an NaOH solution with a pH value of 14 featured pure CuO nanoflowers comprising slightly curled nanosheets with a thickness of approximately 10 nm. This sensor demonstrated excellent H2S sensing performance at room temperature, exhibiting a response value of 1.17 for 10 ppb H2S, along with high selectivity and good long-term stability. However, after exposure to H2S, the resistance of the sensor did not recover to its baseline in air at room temperature. Thermogravimetry results revealed that a temperature of 300 °C was effective for recovery of the sensor. Consequently, the operation temperature of the pH14# sensor was controlled using a micro-hotplate. In the pulse heating mode, the sensor’s response to 100 ppb H2S was 1.5, with a response time of 135 s and a recovery time of 137 s.

Ionic current rectification of non-Newtonian fluids in pH-regulated conical nanochannels

The ionic current rectification (ICR) phenomenon generated by the geometrically asymmetric properties of conical nanochannels has attracted much attention, but previous studies have mainly focused on Newtonian fluids and fixed surface charge densities. In this study, the ICR characteristics of pH-regulated conical nanochannels with non-Newtonian fluids are investigated by numerical simulations, and the effects of solution pH, power-law index, and electrolyte concentration on the ionic current, rectification ratio, axial potential, ionic conductivity, ionic concentration, surface charge density, and radial velocity at the channel tip are discussed. The rectification effect of shear-thinning fluids is significantly lower than that of Newtonian and shear-thickening fluids at high solution pH and electrolyte concentration. At pH = 8, the surface charge density increases only 8.7 times when the electrolyte concentration is increased from 1 mM from 1000 mM. When the electrolyte concentration is 1 mM, the surface charge density at pH = 9 increases almost 30 times compared to that at pH = 5.

A comprehensive electrochemical analysis revealing the surface oxidation behavior difference between pyrite and arsenopyrite

This study systematically investigated the surface oxidation behavior differences between pyrite and arsenopyrite under neutral and alkaline pH conditions using various electrochemical measurements. These measurements include open circuit potential (OCP), cyclic voltammetry (CV), potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and Mott-Schottky analyses. Key electrochemical parameters have been obtained. The OCP, oxidation potential (Eox), and charge transfer resistance (Rct) of arsenopyrite and pyrite declined as the solution pH increased, but oxidation current density (jox) and carrier concentration (ND) increased, suggesting that a high solution pH is thermodynamically and dynamically favorable for the oxidation of both pyrite and arsenopyrite. Compared to pyrite, arsenopyrite has a higher Fermi level, lower OCP and Eox, a larger jox, and a smaller Rct at the same pH conditions, suggesting that arsenopyrite oxidation has a higher thermodynamic preference and occurs at a faster rate than pyrite oxidation under neutral and alkaline pH conditions. This comprehensive study enhances our understanding of the oxidation difference between pyrite and arsenopyrite and offers important guidance for the pyrite-arsenopyrite flotation separation when using the selective surface oxidation method.

Assessing Structures and Solution Behaviors of Molecular and Ionic Cocrystals with a Common Bioactive Molecule: 2,4-Pyridinedicarboxylic Acid with Tranexamic Acid and Nicotinamide.

Cocrystals of 2,4-pyridinedicarboxylic acid (PDA) with either nicotinamide (NTD) or tranexamic acid (TXA) as (PDA)·(NTD) and 2(PDA)·(TXA), respectively, are reported, with the former being a molecular cocrystal and the latter being an ionic cocrystal. Single-crystal structure analyses showed that PDA and its coformers are sustained by neutral and ionic hydrogen bonds. Suspensions of (PDA)·(NTD) resulted in complete conversion to PDA monohydrate after 48 h, while 2(PDA)·(TXA) was thermodynamically stable at a lower pH and showed a 2-fold increase in the PDA concentration, relative to pure PDA monohydrate under similar conditions. Thermal characterization of 2(PDA)·(TXA) displayed a lower melting point and a lower heat of fusion, relative to the pure components. Powder dissolution studies were evaluated for PDA, (PDA)·(NTD), and 2(PDA)·(TXA) and the corresponding physical mixtures. The percent of PDA dissolved rapidly reached near 100% for most cases; however, for 2(PDA)·(TXA), complete dissolution was not achieved, and the amount of PDA dissolved decreased to 85% after 3 h. Instability of 2(PDA)·(TXA) was likely a result of a high solution pH during dissolution, and our results confirm that the solution pH plays a key role in determining the solution behavior and phase stability of the cocrystals.

The Influence of Alkali Cations on the Performance of Pt Electrodes in Kolbe Electrolysis of Acetic Acid

AbstractElectrochemical decarboxylation of carboxylic acids is considered a sustainable method to improve the quality of pyrolysis oil. In this study, we assess the effect of monovalent alkali cations (of the acetates) on the performance of Pt electrodes in acid decarboxylation and the competing OER, using various electrochemical methods. We reveal a strong cation dependence generally following the trend Li+<Na+<K+~Cs+ within a large pH range. Using rotating ring disc electrode measurements, we highlight the strong contribution of the oxygen evolution reaction particularly for electrolytes containing Li+ and Na+ which decreases the selectivity for Kolbe oxidation. In addition, the faradaic efficiency (FE) towards methanol ranges between 16 % (for Li+) and 29 % (for Cs+) at high solution pH (9 or 12). The observed trends are generally explained by a cation‐dependent interfacial pH and surface coverage of acetate, both lowest for Li. This is evident from differences in charge transfer resistance determined by impedance measurements and local pH measurements. Additionally, enhanced dissolution of Pt by Li+ is also proposed. This work highlights that K+ and Cs+ cations favor FE for electrochemical Kolbe oxidation, at relatively low current densities.

Polymer composite membranes as SERS substrate materials: Recyclable and highly stable

Surface-enhanced Raman spectroscopy (SERS), as an emerging molecular-level detection technology, has attracted considerable research attention, especially in the context of substrate materials exhibiting Raman enhancement effects. Membrane materials, owing to their commendable uniformity, stability, and ease of modification, hold a pivotal position in the landscape of SERS substrate materials. However, existing SERS substrates based on membrane materials have limited adaptability to a spectrum of extreme environments, including but not limited to high or low pH, elevated salinity, and corrosive solutions. Additionally, SERS substrate materials are synonymous with “waste” and “high investment” because of their inherent disposable nature. This study introduces a pioneering approach, presenting a polymer composite membrane founded on epoxy resin, cellulose paper, and nanometal particles as a novel SERS substrate material. Given the outstanding stability of epoxy resin, the substrate material exhibits normal functionality in environments ranging from −80 ℃ to 100 ℃, with pH levels spanning 1 to 13, and in highly acidic solutions (concentration ≤3 %) and highly alkaline solutions (concentration ≤0.1 M). Moreover, the cleanability inherent in the polymer composite membrane renders the substrate material recyclable. Experimental findings reveal that even after six repeated uses, the substrate material sustains a stable Raman signal enhancement effect. The integration of recyclability and heightened stability makes this SERS substrate material a promising candidate for real-time monitoring and batch testing in chemical production processes or other complex environments.

Protection of bovine serum albumin through encapsulation in hybrid vesicles

This study focuses on hybrid vesicles (HVs) formed through co-assembly of soy phosphatidylcholine (SPC) and a triblock copolymer (F127). After elucidating the superior stability of HVs over the assemblies of neat SPC and F127, these were encapsulated with bovine serum albumin (BSA), as model a thermolabile protein. Characterizations were performed using dynamic light scattering (DLS), electron microscopy, circular dichroism and high-sensitivity differential scanning calorimetry. The size of HVs increased slightly at higher proportion of F127 and upon encapsulation of BSA. In spite of this, vesicles remained spherical and displayed a smooth surface. They showed superior dilution stability in comparison to neat copolymer micelles and phospholipid vesicles. Their stability can be ascribed to hydrophobic association between the phospholipid and copolymer, and manifested into increase in phase transition temperature of the former. We found that HVs could protect BSA from denaturation and unfolding when challenged by high solution temperature, pH changes and salt incorporation.

Understanding the setting behaviours of alkali-activated slag from the dissolution-precipitation point of view

Ground granulated blast-furnace slag (GGBS) is widely used as supplementary cementitious material of interest for adjusting the performance of concrete. Unlike standard commercial products, characteristics of GGBS from different iron manufacturers vary significantly and assessment of its reactivity, especially at an early age, is not well-established despite numerous parameters specified in current standard systems. Three GGBSs with different setting features during the alkali-activated process were dissolved in either deionised (DI) water or NaOH solution in this study. To illustrate the fundamental processes of reaction kinetic, the dissolved ion concentrations, glassy structural changes, and chemically bound water were measured using ICP-OES, FTIR, and TG respectively. Meanwhile, thermodynamic calculations were carried out to estimate the precipitation of C–S–H gels, which is directly linked with setting behaviours. The results clearly show the differences in the dissolution of the three GGBSs, which could be used to indicate the activity of GGBS. The GGBS with higher activity (i.e. faster setting during alkali activation) tends to dissolve evenly in DI water, whilst those with lower activity show that the silicate groups with lower polymerisation dissolved faster. The chemically bound water determined by TG analysis and the effective saturation index (ESI) are promising parameters for reflecting the activity of GGBS during dissolution in the alkali media. Although this study demonstrated the dissolution rate of higher polymerised silicate groups in GGBS should be the root for the differences in its activity, more structural information on the glassy phase and the interactions of alkali with the surface of GGBS still require further understanding. It is speculated that the ratio of Al[IV]/Al[V] plays an important role in the activity of GGBS. This finding may shape a certain basic understanding of how GGBSs dissolve in neutral and high pH solutions and highlight a re-evaluation of assumptions in thermodynamic simulation under different conditions.

Effect of pH on the Structure, Functional Properties and Rheological Properties of Collagen from Greenfin Horse-Faced Filefish (Thamnaconus septentrionalis) Skin.

Collagen is an important biopolymer widely used in food, cosmetics and biomedical applications. Understanding the effect of pH on the structure and properties of collagen is beneficial for its further processing and exploitation. In this study, greenfin horse-faced filefish skin collagen (GHSC) was prepared and identified as a type I collagen. We systematically investigated the effect of pH on the structural, functional and rheological properties of GHSC. Scanning electron microscopy showed that the collagen morphology changed from an ordered stacked sheet structure to a rough silk-like structure as pH increased. Gaussian-fitted Fourier infrared spectroscopy results of the collagen revealed that it unfolded with increasing pH. Moreover, the ordered structure was reduced, and random coils became the dominant conformation. Its β-sheet and random coil contents increased from 18.43 ± 0.08 and 33.62 ± 0.17 to 19.72 ± 0.02 and 39.53 ± 1.03%, respectively, with increasing pH. α-helices and β-turns decreased from 35.00 ± 0.26 and 12.95 ± 0.01 to 29.39 ± 0.92 and 11.36 ± 0.10%, respectively. The increase in β-sheets and random coils allowed the pI-treated collagen to exhibit maximum water contact angle. The emulsification and foaming properties decreased and then increased with increasing pH in a V-shape. The increased net surface charge and β-sheets in collagen benefited its emulsification and foaming properties. The rheological results showed that the protoprotein exhibited shear-thinning properties in all pH ranges. The collagen solutions showed liquid-like behaviour in low-pH (2, 4) solutions and solid-like behaviour in high-pH (6, 7.83 and 10) solutions. Moreover, the frequency-dependent properties of the storage modulus (G') and loss modulus (G″) of the collagen solutions weakened with increasing pH. Collagen has considerable frequency-dependent properties of G' and G″ at low pH (2, 4). Thus, the importance of collagen raw material preparation for subsequent processing was emphasised, which may provide new insights into applying collagen-based materials in food, biomaterials and tissue engineering.

Selective sodium removal with electrodialysis by modifying concentration gradients using EDTA complexation

Circular water reuse is often limited by the accumulation of harmful ions and the loss of valuable ions during water desalination. Selective removal of specific ions from water is essential but challenging with conventional desalination technologies, especially for ions with similar properties, such as sodium (Na+) and potassium (K+). In the present study, the use of electrodialysis in combination with EDTA complexation in the concentrate is proposed to selectively remove Na+ ions from a multi-ionic solution containing Na+, K+, and NO3− ions. Electrodialysis experiments were conducted at lab-scale at different operational conditions (i.e. solution pH, applied voltage, EDTA/Na+ ratio and solution ion composition) to evaluate the selectivity of the proposed process. It was found that a high solution pH (>10) and a low applied voltage (<0.3 V per cell pair) is required to maximize the selective transport of Na+ ions, while the presence of other metal ions in solution limits the process efficiency. The effect of the proposed process on the transport mechanisms in electrodialysis, which are electromigration, convection and diffusion, was also examined. The provided analysis concluded that the electromigration and convection mechanisms show the largest contribution to the transport of both Na+ and K+ ions, while the process selectivity is controlled by selective diffusion of ions which is enhanced by EDTA complexation. Finally, the regeneration and recovery of EDTA with acidification was experimentally evaluated at different pH values and different precipitation times; recoveries of >95 % were achieved with an acidic solution with pH < 2 in 30 min.

Water extractability of the zinc protoporphyrin IX–myoglobin complex from Parma ham is pH-dependent

The bright red color of Parma ham is mainly derived from zinc protoporphyrin IX (ZnPP), which exists in both water-soluble and insoluble states. Water-soluble ZnPP mainly binds to hemoglobin, however, the presence of water-insoluble ZnPP remains unexplained. Therefore, we aimed to elucidate how ZnPP exists in a water-insoluble state by focusing on its binding substance. Depending on the skeletal muscle, water-insoluble ZnPP comprised 30–50% of total ZnPP. The ZnPP water extractability was positively correlated with muscle pH. Water-insoluble ZnPP was extractable with a high-pH solution and existed as a complex with myoglobin or hemoglobin; nevertheless, myoglobin-binding ZnPP was more abundant. Furthermore, the water solubility of the myoglobin globin moiety at pH 5.5–6.0 was reduced by ZnPP binding. These results suggest that water-insoluble ZnPP mainly exists as a ZnPP–Mb complex, with low solubility attributed to the low pH of the ham.

The corrosion behavior of borosilicate glass in the presence of cementitious waste forms.

Borosilicate glasses are widely used for radioactive waste disposal due to their ability to incorporate a variety of contaminants and radionuclides while exhibiting high durability in various disposal scenarios. This research evaluated the dissolution of borosilicate glass using both single-pass-flow-through (ASTM C1662-18) and product consistency test (ASTM C1285-21) methods with different solutions, including a cementitious-contacted water (called grout-contacted, GC, from this point) and solutions with varying levels of dissolved cementitious species such as Si, Ca, Al. The results indicated that the presence of Ca plays a crucial role in suppressing glass corrosion, as evidenced by the slower normalized dissolution rates, which were one order of magnitude lower for boron and two orders of magnitude lower for rhenium, observed in both Ca-amended and GC solutions compared to the pH 12 buffer solution. This effect is attributed to the formation of a dense, low-porosity, and strongly bonded calcium silicate hydrate (CSH) layer on the glass surface, which implies that a glass corrosion process is influenced by ion exchange involving alkali ions Na+, K+, Ca2+, and hydrogen-containing species. A small number of glass particles treated in the GC solution showed minor corrosion pits in the form of shallow craters with an average diameter of approximately 500 μm. This observation is correlated with a significant reduction, 2000 to 3000 times lower, in the cumulative volume of glass pores, indicating that smaller pore voids were "sealed" in the presence of Ca2+ ions, likely attributed to the formation of CSH precipitation or other corrosion products such as calcium carbonate saturated from the grout solution. These findings suggest that the presence of dissolved Ca in the GC solution can slow down the dissolution of borosilicate glass, contrary to the expected trend of higher dissolution rates resulting from exposure to high alkaline and thus higher pH solutions.

Adsorptive removal of dissolved Iron from groundwater by brown coal – A low-cost adsorbent

Iron (Fe) contamination in groundwater is a widespread issue, necessitating the implementation of efficient removal methods to ensure the provision of safe drinking water. To contribute to the development of effective and sustainable solutions for addressing Fe contamination problems, this study investigated the potential of natural brown coal (BC) as a cost-effective adsorbent for removing dissolved Fe from groundwater. The study also explored the regeneration and reusability potential, as well as the effects of operational parameters, including pH, temperature, adsorbate concentration, and competitive ions, on the adsorption process. The equilibrium data fitted very well with the Langmuir model (R2 = 0.983), yielding a maximum adsorption capacity of 1.41 mg g−1. The adsorption kinetics were well described by the pseudo-second-order kinetic model. Notably, higher solution pH, Fe concentration, and temperature values led to higher Fe removal. The adsorption process exhibited endothermic behaviour, accompanied by an increase in randomness at the interface between the BC and the Fe. The BC was easily regenerated and maintained good adsorption capacity after four cycles of adsorption and regeneration. However, the presence of high-valent cations could affect its performance. Fourier-transform infrared spectrometry, coupled with structural and aqueous solution elemental analyses, revealed a synergetic adsorption mechanism, comprising ion-exchange with mono and divalent basic cations and complexation with functional groups. Overall, these findings highlight the potential of brown coal as a cost-effective adsorbent for Fe removal from groundwater.

Potential mobilization of water-dispersible colloidal thallium and arsenic in contaminated soils and sediments in mining areas of southwest China

Water-dispersible colloids (WDCs) are vital for trace element migration, but there is limited information about the abundance, size distribution and elemental composition of WDC-bound thallium (Tl) and arsenic (As) in mining-contaminated soils and sediments solutions. Here, we investigated the potential mobilization of WDC-bound Tl and As in soils and sediments in a typical Tl/As-contaminated area. Ultrafiltration results revealed on average > 60% of Tl and As in soil solution (< 220 nm) coexisted in colloidal form whereas Tl and As in sediment solution primarily existed in the truly dissolved state (< 10 kDa) due to increased acidity. Using AF4-UV-ICP-MS and STEM-EDS, we identified Fe-bearing WDCs in association with aluminosilicate minerals and organic matter were main carriers of Tl and As. SAED further verified jarosite nanoparticles were important components of soil WDC, directly participating in the migration of Tl and As. Notably, high pollution levels and solution pH promoted the release of Tl/As-containing WDCs. This study provides quantitative and visual insights into the distribution of Tl and As in WDC, highlighting the important roles of Fe-bearing WDC, soil solution pH and pollution level in the potential mobilization of Tl and As in contaminated soils and sediments.

Swelling and hydraulic characteristics of two grade bentonites under varying conditions for low-level radioactive waste repository design

Bentonite is a recommended material for the multiple barriers in the final disposal of low-level radioactive waste (LLW) to prevent groundwater intrusion and nuclear species migration. However, after drying-wetting cycling during the repository construction stage and ion exchange with the concrete barrier in the long-term repository, the bentonite mechanical behaviors, including swelling capacity and hydraulic conductivity, would be further influenced by the groundwater intrusion, resulting in radioactive leakage. To comprehensively examine the factors on the mechanical characteristics of bentonite, this study presented scenarios involving MX-80 and KV-1 bentonites subjected to drying-wetting cycling and accelerated ion migration. The experiments subsequently measured free swelling, swelling pressure, and hydraulic conductivity of bentonites with intrusions of seawater, high pH, and low pH solutions. The results indicated that the solutions caused a reduction in swelling volume and pressure, and an increase in hydraulic conductivity. Specifically, the swelling capability of bentonite with drying-wetting cycling in the seawater decreased significantly by 60%, while hydraulic conductivity increased by more than three times. Therefore, the study suggested minimizing drying-wetting cycling and preventing seawater intrusion, ensuring a long service life of the multiple barriers in the LLW repository.

Enhancing electrocatalytic performance and Stability: A novel Prussian Blue-Graphene quantum dot nanoarchitecture for H2O2 reduction

The reduction reaction of hydrogen peroxide (H2O2) stands as a pivotal electrochemical process holding the promise of revolutionizing energy conversion and water treatment applications. Realizing this potential hinges on the development of electrocatalysts that not only exhibit exceptional activity but also demonstrate unwavering stability. Herein, we propose a pioneering electrocatalyst composed of Prussian blue (PB)-graphene quantum dot (GQD) (PB-GQD) nanoarchitecture fabricated through an in-situ electrochemical method. The PB-GQD nanoarchitecture boasts precisely crafted PB nanoparticles (NPs) that exhibit remarkable electrochemical catalytic activity and stability, offering a substantial advancement over conventional PB NPs structure used as a control. The augmentation of electrocatalytic performance in the PB-GQD nanoarchitecture can be attributed to the symbiotic relationship between PB NPs and GQD. This synergy is engendered through electrostatic attraction and/or coordination interactions between PB precursor’s iron cations and GQD’s multivalent polyanions. This unique arrangement accelerates heterogeneous electron transport, endows the structure with abundant electrochemically active sites, and shortens mass transfer lengths. Notably, GQD’s presence, rich with hydroxyl (–OH) and carboxylic (–COOH) groups, mitigates the decomposition of PB NPs into Fe(OH)3 in neutral or higher pH solutions. This preservation mechanism ensures sustained, elevated electrocatalytic performance for H2O2 reduction.

Impact of Long-Term Exposure to High Chlorine and to Low pH Solutions during Chlorine Regeneration of Ammonia-Loaded Zeolite

An earlier study has shown that chlorine solutions were capable of effectively regenerating an ammonium-loaded zeolite column; however, the chlorine concentrations were high (1000 mg Cl2/L), and for two hours of the regeneration cycle, the pH was approximately 3. This led to concerns regarding the long-term durability of the zeolite. The objective of this study is to investigate the durability of a zeolite by conducting long-term batch exposure tests using (a) high concentration chlorine solutions and (b) low pH solutions. Particle size analysis, SEM images, N2 gas adsorption tests, FTIR characterization and batch loading tests showed that 35-day exposure to 1000 mg Cl2/L solutions did not significantly impact the zeolite studied. This chlorine exposure is equivalent to 840,000 ppm-h, which is three orders of magnitude higher than the values recommended by the supplier. The 90-day-long low pH exposure tests showed that pH = 4 solutions only slightly impacted the zeolite’s characteristics and ammonium uptake; however, the pH = 3 exposure led to discernable changes, and the pH = 2 exposure led to an even greater impact. At pH = 2, there was a breakdown of some external part of the zeolite particles, leading to a 7.1-fold increase in the fines and a 56% reduction in the ammonium uptake. The decrease in the ammonium uptake was proportional to the percent of fines.

The long-term performance of a bituminous geomembrane (BGM) under single-sided exposure conditions

A custom-designed apparatus (referred to as the Ageing Column) is used to age a 4.8-mm thick elastomeric bituminous geomembrane (BGM) under single-sided exposure to a synthetic municipal solid waste (MSW) leachate and a synthetic high pH mining solution (pH 11.5) at 55 °C, 70 °C, and 85 °C. This apparatus involves a closer simulation of the BGM's chemical exposure conditions in the field than the double-sided immersion tests in which the BGM is exposed to the solution from both surfaces. The mechanical, rheological, and chemical properties of the BGM are examined to assess the degradation in the BGM components relative to double-sided immersion experiments. While the single-sided ageing of the BGM reduces the degradation rates in the BGM mechanical properties, it does not affect the degradation rate of the bitumen coat relative to the double-sided exposure. Additionally, the exposure of the BGM to the MSW leachate resulted in faster degradation in its mechanical properties but slower degradation in the bitumen coat than that obtained in the exposure to the mining solution. However, predictions of the time to nominal failure of the BGM established using Arrhenius modelling at different temperatures show that the temperature effect is more significant on the BGM durability than the chemistry of the considered solutions.

INHIBITION PROFICIENCY OF Al 3+ ON MILD STEEL CORROSION IN DIFFERENT pH AQUEOUS MEDIUM

The effect of pH on the inhibition performances of Al3+ on mild steel corrosion in Cl- aqueous solution has been investigated by immersion tests and electrochemical tests. Immersion tests results showed that the rate of corrosion in higher pH solution was decreased as compared to the lower and intermediate pH. Scanning electron microscopic observation elucidated that the lower number of pits and grain boundaries on the sample immersed in higher pH solution as compared to lower pH solutions. The electrochemical impedance spectroscopic results showed the highest charge transfer resistance in higher pH solution, and supported the results obtained from the immersion tests. X-ray photoelectron spectroscopic results elucidated a protective layer was formed on the steel surface immersed in the higher pH solution that was associated with Al(OH)3. Therefore, it was suggested that the protective layer on the steel surface immersed in the higher pH solution inhibited the corrosion reactions.

Construction of molecular enrichment accelerators via assembly of enzyme surface grafted polymer and cyclodextrin achieving rapid and stable ester catalysis for biodiesel synthesis

Efficient and stable catalysis has always been the core concept of enzyme catalysis in industrial processes for manufacturing. Here, we constructed molecular enrichment accelerators to synergistically enhance enzyme activity and stability by assembling enzyme surface grafted polymer and cyclodextrin. At 40 °C, the enzyme activity of CalB-PNIPAM212/β-CD was 2.9 times that of CalB-PNIPAM212. The enzyme activity of CalB-PNIPAM428/γ-CD had reached 1.61 times that of CalB. At the same time, the stability of CalB-PNIPAM212/β-CD and CalB-PNIPAM428/γ-CD are slightly better than that of CalB under high temperature, organic solution and extreme pH conditions. The synergistic increase in activity and stability of the lipase-polymer assembly was achieved due to the structure of assembly, in which the role of cyclodextrin could enrich substrate affecting molecular diffusion. In addition, the lipase-polymer assembly proved to be an efficient catalyst for biodiesel synthesis, with a biodiesel conversion 1.4 times that of CalB at 60 °C. Therefore, this simple and low-cost lipase-polymer assembly provides new possibilities for the construction of high-efficiency industrial biocatalytic catalysts.