Second-order Kinetic Equation Research Articles

Direction of changes in porous structure and adsorption capacity during topochemical oxidation of coal activated by alkali

The purpose of the work is to evaluate the influence of topochemical oxidation (H2O2, HNO3) of carbon prepared by alkali activation of coal on porosity and ability to adsorb 4-chlorophenol (CPh), Pb(II) cations and iodine. Carbons were oxidized at the reactant/carbon ratio of 1:1 (mol/mol, 250С, 24 h). Based on nitrogen adsorption-desorption isotherms, the volumes and specific surfaces of ultramicro- (Sumi), supermicro- (Ssmi) and other pores were evaluated. Kinetics and adsorption isotherms (250С) of CPh and Pb(II) were characterized; adsorption capacities of CPh, Pb(II) and I2 were determined. The H2O2-assisted modification was found to significantly increase Sumi (from 615 to 829 m2/g), but decrease Ssmi (from 515 to 494 m2/g). The HNO3-assisted modification slightly increases Sumi (from 615 to 651 m2/g), does not change Ssmi, but forms mesopores. The CPh adsorption is best approximated by the second-order kinetics, and isotherms are well fitted with the use of the Langmuir model. The H2O2 treatment increases the CPh capacity from 314 to 389 mg/g; and the НNO3 modification significantly decreases the CPh capacity (to 189 mg/g). Modifications reduce the iodine capacity by 1.11 times (H2O2) and 2.33 times (HNO3). The Pb(II) absorption was established to describe by the second-order kinetics equation; the adsorption isotherms obey Langmuir (R20.986) and Freundlich (R20.984) models. The Pb(II) capacity slightly increases after H2O2-assisted modification (from 87 to 95 mg/g), but increases sharply (from 87 to 298 mg/g) after HNO3-assisted treatment because of significant increasing OH-acidic groups concentration.

Numerical simulations of the flow of a kerosene gel: Effects of thixotropy and shear-thinning

The ability of a gel to act like a solid-like material at rest and flow like a liquid when sheared can be very useful in propulsion system. Numerical simulation of the flow of gel fuels can be used as a reference to assist experimental studies and applications of these materials. Non-linear rheological effects such as shear thinning, yield stress, thixotropy and viscoelasticity can create difficulties in the formulation and in the numerical investigations. This paper uses a thixotropic shear-thinning constitutive relationship while using a second-order kinetic equation for the structural parameter, where the Carreau–Yasuda model is used for a 5% organic kerosene gel. We study the simple shear flow to verify the accuracy of the numerical method, and the impact of the constitutive parameters on the apparent viscosity as a function of shear rate. To look at the thixotropic flow in more complex flows, we initially study the pipe flow of an organic kerosene gel for different pumping conditions. After performing a parametric study, we find that the thixotropy of the gel strongly affects the shear history, that is, the nonuniform aging distribution. The destruction of the microstructure can be accelerated by adjusting the flow intensity and the model parameters, but it seems that it is difficult to arrive at the equilibrium state within the time scale of the propulsion system; this poses a challenge to the design of the system.

Two-Stage Residual Lifespan Prediction Model for Oil-Paper Insulation Based on Analysis of Furfural and Methanol in Oil

The applicability of existing single aging indicator-based lifespan prediction methods needs further improvement during different aging stages. Considering the aforementioned challenges, this work proposes a two-stage residual lifespan prediction model based on both methanol and furfural. Firstly, the changes in methanol and furfural contents in oil are examined concurrently with the aging duration. The paper insulation's life is divided into different aging stages by using identified two demarcation points according to the indicator's content. By virtue of this, the two-stage residual lifespan model of the insulating paper is obtained by coupling with the second-order aging kinetic equation. Finally, the validity of the proposed model is proved through a comparison to the conventional method of utilizing a single indicator, with a mean absolute percentage error for insulating paper's residual lifespan of 5.6%. In that regard, the research's contribution is to propose an integrated model for predicting the residual lifespan of insulating paper by using methanol and furfural indicators.

Hollow polyester/kapok/hollow polyester fiber-based needle punched nonwoven composite materials for rapid and efficient oil sorption.

Nowadays oil pollution poses a serious threat to the environment and people's daily life. As reusable and environmentally friendly materials, fiber-based oil sorption materials can effectively alleviate this phenomenon. However, maintaining a high sorption rate along with improved mechanical properties remains a challenge for oil sorption materials. Herein, we report a novel hollow PET/kapok/hollow PET nonwoven with high porosity and oil retention, outstanding cyclic oil sorption rate and improved mechanical performance using kapok as the oil preserver and hollow PET as the conductor and structure enhancer. Benefiting from the three-layer composite structure fabricated by carding and needle punching reinforcement, the resulting oil sorption materials, with kapok proportion more than or equal to 60%, exhibited high oil sorption rate and oil sorption speed. The materials of 20HP/60K/20HP component content present a high initial oil sorption rate of 28.22 g g-1, a maximum oil sorption rate of 31.17 g g-1 and a sorption rate constant of the Quasi second-order kinetic equation of 0.067 in plant oil. On the other hand, when the proportion of kapok fiber in the material was below 60%, due to the introduction of hollow PET, the mechanical properties were significantly boosted, and its oil retention and reusability were distinguished, with a reuse rate stabilizing at a relatively high level (>93%) in plant oil after undergoing three oil sorption cycles. The successful fabrication of hollow PET/kapok/hollow PET nonwovens could provide a new approach for the design and development of oil sorption materials.

Removal of gaseous elemental mercury using corn stalk biochars modified by a green oxidation technology

Straw biochars are the widely used carbon materials for adsorbing gaseous Hg0 due to developed porous structure. However, its application is restricted by scarcity of active sites on carbon surface. Existing modification methods such as acids, halides, sulfides, metal oxides, etc. have problem of secondary pollution. In this work, a corn stalk biochar modified with UV/H2O2 green modification technology was prepared to capture gaseous Hg0 for the first time. The physicochemical properties of the adsorbent and the effect of several key parameters containing H2O2 concentration, adsorption temperatures and common gas components on gaseous Hg0 capture were studied. The kinetic process and mechanisms of gaseous Hg0 adsorption were also expounded. Research indicated that through producing ·OH free radicals with high activity, UV/H2O2 green modification technology could not only improve pore structure of corn stalk biochar, but also make containing-O functional group more abundant on carbon surface, promoting gaseous Hg0 adsorption. Optimal H2O2 modification concentration and adsorption temperature are 3 wt% and 120 °C, respectively. The capture process of gaseous Hg0 accorded with quasi second-order kinetic equation. Chemisorbed oxygen (O*) and CO functional group show pivotal roles in the capture processes of gaseous Hg0.

Adsorption Characteristics of Iron on Different Layered Loess Soils.

In view of the problem of Fe3+ pollution in an iron sulfur mine, different layers of loess soil in the Bijie area were used for adsorption to alleviate the mine wastewater pollution by natural treatment. The effects of the initial concentration of Fe3+, adsorption time and pH value on the adsorption performance of top, core and subsoil layers of loess soils were studied by the oscillatory equilibrium method, and the adsorption mechanism of these three soils was analyzed through a kinetic adsorption experiment and infrared spectroscopy. The results showed that the adsorption capacity of Fe3+ was improved by increasing the initial concentration and reaction time, but the adsorption rate of the adsorption capacity of Fe3+ was reduced. The adsorption rate of Fe3+ in the subsoil layer was faster than that in the other two layers. The higher the pH, the higher the adsorption capacity. After the pH was higher than 3.06, it had little effect on the adsorption capacity, but the adsorption rate increased. The first-order kinetic equation, second-order kinetic equation and Elovich equation were suitable for iron adsorption kinetics of three soils. The fitting correlation coefficient of the second-order kinetic equation was close to one, indicating the main role of chemical adsorption. The adsorption rate constant of the subsoil layer was about two times and three times that of the core soil layer and the topsoil layer. The Langmuir model can better fit the isothermal adsorption process. The results of infrared spectroscopy of soil showed that the content of soil organic matter played an important role in the adsorption capacity of Fe3+. The subsoil layer had a higher concentration of organic matter and more abundant functional groups, so the adsorption capacity of Fe3+ was the highest. The results could provide a theoretical basis for the removal of iron in acid mine wastewater.

Synthesis and characterization of noble hydrogel beads of amino functionalized reduced graphene oxide for selective extraction of gold from electronic waste

For a sustainable future, the rapid increase in the use of electrical and electronic devices necessitates new technologies and methods for the recovery and recycling of electronic waste. The selective extraction of gold from e-waste was achieved using amine-functionalized reduced graphene oxide impregnated in calcium alginate matrix (NH 2 -rGO-Ca-Alg). The NH 2 -rGO-Ca-Alg hydrogel beads were characterized using SEM-EDS, XRD, Zeta potential, ATR-FTIR and Raman spectra. Highly efficient gold extraction (above 96 percent absorption of gold at pH ranges 2-4) was evaluated in batch sorption investigations. The sorption of gold using NH 2 -rGO-Ca-Alg beads requires an equilibrium contact time of 24 hours. Using the Langmuir isotherm model, the maximal sorption capacity of the NH 2 -rGO-Ca-Alg beads was determined to be 12.48 mg g-1. From the kinetic study, sorption was observed to follow a second-order pseudo kinetic equation. Experimental observation of intraparticle diffusion revealed that gold sorption on the NH 2 -rGO-Ca-Alg beads takes place in three stages. Additionally, gold was leached from a junk solid-state detector using aqua regia, and the NH 2 -rGO-Ca-Alg beads demonstrated highly effective and selective gold extraction from the leached solution. The elemental spectra of the NH 2 -rGO-Ca-Alg beads after gold sorption shows gold peaks and uniform distribution of gold on the bead surface was observed using elemental mapping. • Amino functionalised reduced graphene oxide was infused in calcium alginate to form hydrogel beads. • NH 2 -rGO-Ca-Alg beads sorption of Gold was almost constant in the pH range of 2-6. • Sorption capacity of the NH 2 -rGO-Alg beads was calculated as 12.58 mg g -1 from Langmuir isotherm model • Intra particle diffusion of Au ions on the beads was “multilinear nature”.

Non-thermal treatments for the control of endogenous formaldehyde from Auricularia auricula and their effects on its nutritional characteristics

To control endogenous formaldehyde (EFA) from Auricularia auricula and preserve its nutritional properties, we selected various non-thermal treatments and evaluated their effects on the removal of EFA, inhibition of γ-glutamyl transpeptidase and l -cysteine sulfoxide lyase activities, and bioactive ingredients (i.e., principal nutrients, including vitamins and taste substances). The results showed that single and co-non-thermal treatments (US-EW, IPL-EW) reduced the EFA content of A. auricula to varying degrees. Correlation and principal component analyses showed that synergistic treatment with ultrasound and electrolyzed water (US-EW) significantly reduced EFA (removal rate = 40.54%), with relatively small losses of other chemical components. The second best was treatment with intense pulsed light and electrolyzed water (IPL-EW) (removal rate = 36.27%). We constructed and validated a kinetic model for EFA removal using the US–EW treatment, and fitted a second-order kinetic equation. The optimal process parameters were as follows: ultrasound (US) frequency: 50 kHz, US power: 100 W, and available chlorine concentration of EW: 35 mg/L. These results were verified and can serve as a reliable technical reference to improve safety during the processing and preservation of edible fungi. • US-EW has the highest removal rate of EFA (40.54%). • The removal of EFA via US-EW confirmed the second-order reaction kinetic. • The optimal processing parameters for US-EW removal of EFA have been obtained. • US-EW causes the least loss in nutritional quality of A. auricula .

Preparation and Adsorption Performance of Cellulose Acetate Fiber-Chitosan/Titanium Dioxide Surface Layers Composite Membranes Prepared Based on a Sol-Gel Method

CA/CS/TiO2 composite membranes were formed by cellulose acetate (CA) electrospun fibers which were used as the basal layer, and chitosan (CS)/sol-gel titanium dioxide (TiO2) which was coated as a surface layer on one side. The composite membrane exhibited a smooth and flat surface when the CS:TiO2 ratio was 10:1 (mass ratio) and the CA:CS ratio was 12:10 (volume ratio). This layered structure of the membrane exhibited a water flux of 119 L/(m2·h). Adsorption testing of this composite membrane for dyes showed that the adsorption capacities of methylene blue and rhodamine were 42 and 51 mg/g, respectively. The composite membrane showed better adsorption performance for rhodamine mainly because of the bonding between the hydroxyl groups of CS and TiO2 and the carboxyl groups of the rhodamine dye. The adsorption processes of the two dyes were in accord with a second-order kinetic equation.

Surface Modification of Biomass with Di-(2-Ethylhexyl)phosphoric Acid and Its Use for Vanadium Adsorption.

The method of carbonizing biomass using di-(2-Ethylhexyl) phosphoric acid and tributyl phosphate impregnation (SICB) was studied in this research. SICB combines the benefits of an extractant and an ion exchange resin. The adsorption and desorption properties of vanadium were investigated, and the adsorption mechanism was analyzed. The results showed that the carrier was first prepared at a temperature of 1073.15 K using sawdust as a biomass substitute and then cooled to room temperature. The best adsorption performance was obtained by impregnating the carriers with di-(2-Ethylhexyl) phosphoric acid and tributyl phosphate for 60 min. The vanadium adsorption rate of 98.12% was achieved using the biomass at an initial V(IV) solution concentration of 1.1 g/L, a pH value of 1.6, and a solid-to-liquid ratio of 1:20 g·mL for 24 h. Using 25 wt.% sulfuric acid solution as desorbent, the desorption rate of vanadium was as high as 98.36%. The analysis showed that the adsorption of vanadium by SICB was chemisorption, and the adsorption process was more consistent with the proposed second-order kinetic equation. Therefore, SICB has high selectivity and high saturation capacity because of the mesopores and micropores produced by carbonization.

Cyanide Release Characteristics of Solid Waste in Gold Smelting Process

To explore the relationship between total cyanide and easily liberatable cyanide in cyanide tailings and its impact on the environment, the leaching and release characteristics of total cyanide and easily liberatable cyanide in a tailings pond were studied using a dynamic leaching experiment, and a dynamic model was established. The results show that the release concentration of total cyanide in cyanide tailings is higher than that of easily liberatable cyanide. With the increase in leaching time, the release of cyanide is more sensitive to leaching intensity. The first-order kinetic, second-order kinetic, modified Elovich, double constant, and parabolic diffusion equations were used to fit the cumulative release of cyanide. According to the kinetic results of cyanide cumulative release, in addition to the first-order kinetic equation, the other four equations revealed good fitting for the cyanide leaching process, which shows that cyanide released under simulated rainwater leaching was not simply via surface diffusion, but controlled by multiple factors.

Enhanced biosorption of europium and cesium ions from aqueous solution onto phalaris seed peel as environmental friendly biosorbent: Equilibrium and kinetic studies

The sorption characteristics of Eu(III) and Cs(I) removal from aqueous solution were estimated using phalaris seeds peel powder (PSP), a novel biosorbent that is economical and low-cost. Batch equilibrium experiments were carried out to investigate the effects of contact time, initial metal concentration, media pH, and interference ions on the sorption of Eu(III) and Cs(I). PSP powder characterization via Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG/DSC), X-ray diffraction (XRD), and scanning electron microscope (SEM) revealed some changes before and after the adsorption process. This indicates that most likely, adsorption has taken place between the metal ions and the adsorbents in the aqueous solution. The obtained results show that Eu(III) has a higher selectivity than Cs(I). The kinetics of the adsorption of Eu3+ and Cs+ have been discussed. It was shown that the second-order kinetic equation could describe the sorption and was found to be the best fitted model (R2 = 0.999) for two metal ions. Langmuir and, Dubinin–Radushkevich (D–R), isotherm were found to best fit (R2 = 0.99) in this study. The separation factor (RL) value of less than 1.0 indicates that the biosorption of both metal ions on PSP is favorable. Thermodynamic parameters, such as ΔHo, ΔGo, and ΔSo, have been calculated by using the thermodynamic equilibrium coefficient obtained at different temperatures. The obtained results indicated the endothermic nature of the sorption process for both metal ions onto PSP. PSP powder has the potential to be used as a low-cost biosorbent for the removal of Eu(III) and Cs(I) from wastewater, according to the findings.

Adsorption properties and mechanism research of phosphorus with different molecular structures from aqueous solutions by La-modified biochar.

In order to explore the adsorption characteristics of phosphorus from molecules with different molecular structures and varying number of phosphate groups on metal-modified biochar, walnut shell biochar was modified with LaCl3 to prepare lanthanum-loaded biochar (BC-La). Adsorption of four polar components, namely phytic acid (IHP), adenosine-5'-disodium triphosphate (5-ATP), hydroxyethylidene diphosphonic acid (HEDP), and sodium pyrophosphate (PP), was studied. The adsorption properties and mechanism of phosphorus sorption by BC-La were analyzed by SEM-EDS and FTIR for the different structures. The results showed that the maximum adsorption capacity of BC-La for IHP, 5-ATP, HEDP, and PP was 85.85, 9.04, 15.80, and 14.45mg/g, respectively. The adsorption capacity was positively correlated with the polarity of organic phosphorus. The adsorption behavior conformed to the quasi second-order kinetic fitting equation, and the increase of temperature was conducive to the removal of all four phosphorus pollutants. BC-La adsorbs IHP and HEDP mainly through electrostatic attraction. The adsorption of 5-ATP and PP is dominated by complexation. The La-modified biochar has broad prospects in water remediation, which can provide a theoretical basis for removal of different forms of phosphorus pollutants and prevention and control of water eutrophication.

Effect of extraction technique on chemical compositions and antioxidant activities of freeze-dried green pepper.

In this study, the yield, content of piperine, and antioxidant activity of pepper oleoresin obtained with the methods of maceration, ultrasound-assisted extraction (UAE), microwave-assisted extraction (MAE), and ultrasound-MAE (UMAE) were analyzed, and the microstructure of pepper residue was observed. For the yield and piperine content, the UMAE method had the best extraction capacity among the four methods. While, the oleoresin obtained with maceration had the highest total phenolic content, and the antioxidant activity of the oleoresin obtained by maceration was higher than that of the extracts acquired by UAE, MAE, and UMAE, and a high positive correlation was observed between the antioxidant activity and total phenolic content of the oleoresin obtained by these extraction methods. The ideal parameters for UMAE were an 80-mesh particle size and a 1 g/10 mL solid–liquid ratio. The kinetic parameters and models of the UMAE extraction process were also compared using first- and second-order models. The second-order kinetic equation with the lowest root mean square deviation and highest adjusted correlation coefficient proved to be more suitable for describing the extraction kinetics of pepper oleoresin. This study showed that UMAE is a fast, efficient, and cost-effective technique for the extraction of green pepper oleoresin.

Removal of Arsenic from Wastewater by Using Nano Fe3O4/Zinc Organic Frameworks.

Efficient removal of arsenic in wastewater is of fundamental importance due to the increasingly severe arsenic pollution. In this study, a new composite adsorbent (Fe3O4@ZIF-8) for As(V) removal from wastewater was synthesized by encapsulating magnetic Fe3O4 nanoparticles into metal organic frameworks. In order to evaluate the feasibility of Fe3O4@ZIF-8 as an adsorbent for As(V) removal, the adsorption properties of Fe3O4@ZIF-8 were systematically explored by studying the effects of dosage, pH, adsorption isotherm, kinetics, and thermodynamics. Additionally, the characterization of Fe3O4@ZIF-8 before and after adsorption was analyzed thoroughly using various tests including SEM-EDS, XPS, BET, XRD, TG, FTIR, and the properties and arsenic removal mechanism of the Fe3O4@ZIF-8 were further studied. The results showed that the Fe3O4@ZIF-8 has a specific surface area of 316 m2/g and has excellent adsorption performance. At 25 °C, the initial concentration of arsenic was 46.916 mg/L, and pH 3 was the optimum condition for the Fe3O4@ZIF-8 to adsorb arsenic. When the dosage of the Fe3O4@ZIF-8 was 0.60 g/L, the adsorption of arsenic by the Fe3O4@ZIF-8 can reach 76 mg/g, and the removal rate can reach 97.20%. The adsorption process of arsenic to the Fe3O4@ZIF-8 can be well described by the Langmuir isotherm model and the second-order kinetic equation. At pH 3 and temperature 298 K, the maximum adsorption capacity of arsenic by the Fe3O4@ZIF-8 was 116.114 mg/g. Through the analysis of thermodynamic parameters, it is proved that the adsorption process of arsenic by the Fe3O4@ZIF-8 is a spontaneous endothermic reaction. The Fe3O4@ZIF-8 has broad prospects for removing As(V) pollution in wastewater, because of its strong adsorption capacity, good water stability, and easy preparation.

The negative dielectric permittivity of polycrystalline barium titanate nanofilms under high-strength kHz-AC fields

Unlike the conventional high-frequency dielectric behavior for which the amplitude of the applied field is too small to cause polarization switching, the dynamically-driven polarization reorientation brings remarkable frequency dependence to the nonlinear electromechanical behaviors of ferroelectric nanofilms. In this study, we developed a thermodynamically consistent phase-field model with an introduced second-order kinetic equation to investigate the dynamics of polarization switching in polycrystalline barium titanate nanofilms under high-strength AC fields. The newly introduced kinetic equation consists of an additional dynamic inertial term that brings about collective resonance of polarization within a certain frequency range. Negative dielectric permittivity is observed in a certain frequency band as the applied frequency varies from 30 to 80 kHz, and the maximum absolute value is reached around 40 kHz. It was demonstrated through microstructure-based analysis that such negative dielectric behavior is inherited from the frequency-dependent polarization switching in the nanograins. It also serves as the mechanism for other observed frequency-dependent physical properties, e.g., the remnant polarization, the piezoelectric coefficient at zero electric field and the coercive field. In addition, we further explored the influence of the damping coefficient in the kinetic equation and the influence of the in-plane strain to such frequency-dependent behaviors. It was found that a higher damping coefficient or applied in-plane strain tends to weaken the occurrence of negative permittivity.

Ultrasound treatment degrades, changes the color, and improves the antioxidant activity of the anthocyanins in red radish

Ultrasonic technology is commonly used to extract anthocyanins from food. This study extracted anthocyanins from red radish (ARR), which were purified using AB-8 macroporous resin. UHPLC-QQQ-MS/MS analysis identified 25 anthocyanins in the ARR, of which pelargonidin-3-(feruloyl)diglucoside-5-(malonyl)glucoside (P3FD5MG), pelargonidin-3-(p-coumaroyl)diglucoside-5-(malonyl)glucoside (P3PD5MG), and pelargonidin-3-(caffeoyl)diglucoside-5-(malonyl)glucoside (P3CD5MG) were the most abundant. Ultrasound treatment at 136–358 W for 120 min decreased the contents of P3FD5MG, P3PD5MG, and P3CD5MG by 19.5%–34.7%, 18.9%–42.7%, and 21.5%–37.3%, respectively. The degradation of P3FD5MG, P3PD5MG, and P3CD5MG increased by applying ultrasound treatment for an extended period and higher power, following a second-order kinetic equation. The degradation process during ultrasound treatment produced p-hydroxybenzoic acid (PHBA) and protocatechuic acid (PA), improving the ferric reducing antioxidant power (FRAP) and 1,1-diphenyl-2-picrylhydrazyl radical (DPPH·) scavenging activity of ARR. Moreover, ultrasound treatment caused degradation of anthocyanins, thereby leading to distinct color changes in the ARR. Therefore, ultrasound treatment should be used cautiously when processing red radish to preserve their color.

Modeling thixotropic break-down behavior of dense anaerobically digested sludge

Abstract Mixing and homogenization in anaerobic digesters are affected by the flow curve of sludge. The aim of this study is to mathematically express the flow curve of dense anaerobically digested sludge behaving as thixotropic and pseudoplastic fluids. Time-dependent changes in two pseudoplastic parameters, i.e., consistency index (µ p) and pseudoplastic index (n), by shear are modeled using a second-order kinetic equation with a coefficient that includes the power function of the shear strain rate. The calculated results are consistent with the experimental results. The kinetic parameters that yielded the ultimate values after shearing were associated with the sludge concentration, unlike the other kinetic parameters.

Study of a Hydrophilic Healing-Promoting Porcine Acellular Dermal Matrix

Sodium hyaluronate (SH) is recognized as the strongest natural humectant, since it contains a large number of hydroxyl and carboxyl groups in its structure, and can absorb 1000 times its own weight of water. The porcine acellular dermal matrix (pADM) has been widely used in biological materials for its biological activities, such as promoting cell proliferation and promoting wound healing. Enhancing the hydrophilic and moisturizing properties of the pADM is expected to further improve its ability to promote wound healing. However, there are no strong chemical bonds between SH and pADM. Therefore, SH was oxidized by sodium periodate in this study, and was further used to cross-link it with pADM. The microstructure, hydrophilicity, moisture retention, degradation and cytotoxicity of pADM cross-linked with different oxidation degrees of oxidized sodium hyaluronate (OSH) were studied. The results show that OSH-pADM maintained the secondary structure of natural collagen, as well as the good microporous structure of native pADM after cross-linking. With increasing oxidation degree, the surface hydrophilicity and moisture retention capacities of OSH-pADM increased; among them, OSH-pADM cross-linked with 40% oxidation degree of OSH was found to have the strongest moisture retention capacity. The hygroscopic kinetics at 93% RH were conformed to the second-order hygroscopic kinetics equation, indicating that the hygroscopic process was controlled by chemical factors. The degradation resistance of OSH-pADM also increased with increasing oxidation degree, and the cytotoxicity of OSH-pADM was acceptable. The in vivo full-thickness wound healing experiments showed that OSH-pADM had an obvious ability to promote wound healing. It can be speculated that OSH-pADM, with its good hydrophilic and moisturizing properties, physicochemical properties and biocompatibility, has great potential for facilitating wound repair.

Effectiveness of agricultural waste in the enhancement of biological denitrification of aquaculture wastewater.

Nitrogen pollution in aquaculture wastewater can pose a significant health and environmental risk if not removed before wastewater is discharged. Biological denitrification uses external carbon sources to remove nitrogen from wastewater; however, these carbon sources are often expensive and require significant energy. In this study, we investigated how six types of agricultural waste can be used as solid carbon sources in biological denitrification. Banana stalk (BS), loofah sponge (LS), sorghum stalk (SS), sweet potato stalk (SPS), watermelon skins (WS) and wheat husk (WH) were studied to determine their capacity to release carbon and improve denitrification efficiency. The results of batch experiments showed that all six agricultural wastes had excellent carbon release capacities, with cumulative chemical oxygen demands of 37.74–535.68 mg/g. During the 168-h reaction, the carbon release process followed the second-order kinetic equation and Ritger-Peppas equation, while carbon release occurred via diffusion. The kinetic equation fitting, scanning electron microscopy, and Fourier transform infrared spectroscopy results showed that LS had the lowest cm and the maximum t1/2 values and only suffered a moderate degree of hydrolysis. It also had the lowest pollutant release rate and cumulative chemical oxygen demand, as well as the most efficient removal of total phosphorous (TP) and total nitrogen (TN). Therefore, we concluded that LS has the lowest potential risk of excess carbon release and capacity for long-lasting and stable carbon release. The WS leachate had the highest TN contents, while the SPS leachate had the highest TP content. In the 181-h denitrification reaction, all six agricultural wastes completely removed nitrate and nitrite; however, SS had the highest denitrification rate, followed by LS, WH, BS, SPS, and WS (2.16, 1.35, 1.35, 1.34, 1.34, and 1.01 mg/(L·h), respectively). The denitrification process followed a zero-order and first-order kinetic equation. These results provide theoretical guidance for effectively selecting agricultural waste as a solid carbon source and improving the denitrification efficiency of aquaculture wastewater treatment.