Pseudo-second Order Kinetic Model Research Articles

EFFECT OF AMMONIA-ETHANOL MOLE RATIO ON THE SILICA NANOPARTICLES SYNTHESIZED FOR RHODAMINE B DYES ADSORPTION

Various ammonia-ethanol mole ratios were successfully used for the synthesis of silica nanoparticles for rhodamine B adsorption. This study aims to determine the characteristics of the adsorbent at different ammonia-ethanol mole ratios, maximum adsorption at pH, and contact time. Several steps, including extraction of Na2SiO3 from rice husk ash, synthesis of adsorbents with ammonia-ethanol mole ratios (14:1, 21:1, 28:1, and 42:1), and their characterization. The parameters studied in the adsorbent include the functional groups, particle size, maximum pH, and rate constant adsorption. The FTIR results showed that all adsorbents had functional groups, indicating the presence of silica. The results suggest that the optimum mole ratio of NS 14:1 particles has a size of 39.82 nm. The optimum adsorption of rhodamine B by NS 14:1 occurred at a pH 3 of 0.00419 mmol.g-1 and a contact time of 40 min. The rate constant of adsorption by NS 14:1 was 102.42 g.mmol-1.min-1 followed a pseudo-second order kinetic model.

Effective removal of metformin from water using an iron-biochar composite: Mechanistic studies and performance optimisation

Metformin (MF) is widely used in the prevention and treatment of Type 2 diabetes and gestational diabetes. Following its medical administration, it may pass through the body and be introduced into the wastewater treatment system. However, conventional treatment plants are ineffective in removal of MF from wastewater resulting in its introduction into the aquatic environment. Novel and effective methods of MF removal are therefore required to prevent contamination of natural waters. In this work, a magnetised iron-biochar composite derived from brewery waste (magnetic brewery spent grain; MBSG) was generated and evaluated for its ability to remove MF from aqueous media. Response surface methodology (RSM) was applied to identify optimal adsorption parameters. Extensive instrumental characterisation including XPS, FTIR, EPR, Raman spectroscopy and SQUID were used in conjunction with kinetic, isotherm and thermodynamic studies to determine that H-bonding, electrostatic attraction and so-called π-π (electron donor-acceptor) EDA interactions were the mechanisms involved in the adsorption processes. Modelling showed that the MF adsorption was best described by both the Langmuir and the Freundlich models, with the value of qmax = 15.2 mg/g governed by the pseudo-second order kinetic model; and it was a spontaneous (∆G = −17.7 kJ/mol) and endothermic (∆H =38.5 kJ/mol) process. Desorption studies were conducted to evaluate the potential for regeneration and reuse of the material. These demonstrated citric acid (0.2 M) to have significant potential as a regenerative reagent, but that further optimisation is required. This work revealed that MBSG could be a sustainable and effective adsorbent for the removal of aqueous MF in water treatment.

Box–Behnken design with desirability function for methylene blue dye adsorption by microporous activated carbon from pomegranate peel using microwave assisted K2CO3 activation

This research aims to convert pomegranate peel (PP) into microporous activated carbon (PPAC) using a microwave assisted K2CO3 activation method. The optimum activation conditions were carried out with a 1:2 PP/K2CO3 impregnation ratio, radiation power 800 W, and 15 min irradiation time. The statistical Box–Behnken design (BBD) was employed as an effective tool for optimizing the factors that influence the adsorption performance and removal of methylene blue (MB) dye. The output data of BBD with a desirability function indicate a 94.8% removal of 100 mg/L MB at the following experimental conditions: PPAC dose of 0.08 g, solution pH of 7.45, process temperature of 32.1 °C, and a time of 30 min. The pseudo-second order (PSO) kinetic model accounted for the contact time for the adsorption of MB. At equilibrium conditions, the Freundlich adsorption isotherm describes the adsorption results, where the maximum adsorption capacity of PPAC for MB dye was 291.5 mg g−1. This study supports the utilization of biomass waste from pomegranate peels and conversion into renewable and sustainable adsorbent materials. As well, this work contributes to the management of waste biomass and water pollutant sequestration.

Investigation of the performance of activated carbon cloth to remove glyphosate, glufosinate, aminomethylphosphonic acid and bialaphos from aqueous solutions by adsorption/electrosorption.

The present study investigates the removal of glyphosate, glufosinate, aminomethylphosphonic acid and bialaphos herbicides from their 5 × 10-5M aqueous solutions onto activated carbon cloth by adsorption and electrosorption. Analysis of these highly polar herbicides was achieved by UV-visible absorbance measurements, after derivatization with 9-fluorenylmethyloxycarbonyl chloride. The limit of quantification values of glyphosate, glufosinate, aminomethylphosphonic acid and bialaphos were 1.06 × 10-6mol L-1, 1.38 × 10-6mol L-1, 1.32 × 10-6mol L-1 and 1.08 × 10-6mol L-1, respectively. Glyphosate, glufosinate, aminomethylphosphonic acid and bialaphos were removed from their aqueous solutions with higher efficiencies by means of electrosorption (78.2%, 94.9%, 82.3% and 97%, respectively) than of open-circuit adsorption (42.5%, 22%, 6.9% and 81.8%, respectively). Experimental kinetic data were fitted to pseudo-first order and pseudo-second order kinetic models. It was determined that pseudo-second order kinetic model represents experimental data better with satisfactory coefficient of determination, r2 (> 0.985) and normalized percent deviation, P (< 5.15) values. Adsorption isotherm data were treated according to Freundlich and Langmuir isotherm models. Based on the r2 (> 0.98) and P (< 5.9) values, it was found that experimental data well fitted to Freundlich isotherm model. Adsorption capacities of activated carbon cloth for glyphosate, glufosinate, aminomethylphosphonic acid and bialaphos, expressed in terms of Freundlich constant, were calculated as 20.31, 118.73, 239.33 and 30.68mmolg-1, respectively. The results show that the studied ACC can be used in home/business water treatment systems as an adsorbent due to its high adsorption capacity.

Statistical Modelling of Biosorptive Removal of Hexavalent Chromium Using Dry Raw Biomasses of Dioscorea rotundata, Elaeis guineensis, Manihot esculenta, Theobroma cacao and Zea mays

Hexavalent chromium [Cr (VI)] is a highly toxic and hazardous contaminant that poses serious health risks to both humans and the environment. Its presence in water sources can lead to severe health issues, including various types of cancer and respiratory ailments. Therefore, developing efficient and effective methods for Cr (VI) removal is crucial in ensuring safe and clean water supplies. The aim of this research is the environmentally responsible elimination of hexavalent chromium by bioadsorption using corn residues (CR), palm fiber (PF), and the peels of yam (YP), cassava (CP), and cocoa (CH). The study was conducted with varying levels of pH, bioadsorbent quantity, temperature, and adsorbent particle size at 200 rpm, with an initial concentration of 100 mg/L and 24 h of contact time to improve the adsorption efficiency. The process variables were evaluated and optimized using the statistical technique response surface methodology (RSM). The SEM-EDS analysis revealed that the predominant elements in the structure of the bioadsorbents were carbon and oxygen. Furthermore, the adsorption process led to the incorporation of Cr (VI) into the structure of the biomaterials, as indicated by their EDS spectra. The maximal adsorption efficiency of 99.11% was obtained at pH 2, bioadsorbent dose of 0.03 mg, 30 °C, and 0.5 mm of particle size. Various equilibrium isotherms were utilized to fit and analyze the adsorption data. The assessed maximum adsorption capacities were 38.84, 56.88, 52.82, 138.94, and 240,948.7 mg/g for YP, PF, CP, CH, and CR, respectively. The adsorption data exhibited conformity with the Freundlich and Redlich–Peterson isotherm models (R2 = 0.95), indicating that the phenomenon occurs in a multilayer. Pseudo-second order and Elovich kinetic models adjusted the kinetics of chromium (VI), suggesting that the mechanism could be controlled by chemisorption. Therefore, the residual biomasses evaluated can serve as a cost-effective adsorbent for Cr (VI) removal, and the use of RSM enables efficient modeling and prediction of the adsorption process.

Removal of Reactive Red 195 and Methylene Blue dyes by adsorption on the surface of cobalt hydroxide-supported polystyrene waste particles

Waste-derived polystyrene microparticles loaded with cobalt hydroxide were prepared and tested as adsorbents for water treatment. The structure of the obtained adsorbent was analyzed by FT-IR, SEM-EDX and XRD techniques. Two dyes, namely, Reactive Red 195 and Methylene Blue were used to evaluate the adsorption behavior of the adsorbent toward anionic and cationic dyes, respectively. The effects of solution pH, contact time, temperature and adsorbent dose on the adsorption process were investigated. The adsorption data were analyzed using the Langmuir and Freundlich isotherms and the pseudo-first and pseudo-second order kinetic models. The thermodynamic parameters of the adsorption process (changes in enthalpy, entropy, and Gibbs free energy) were estimated. The maximum adsorption capacities estimated using the Langmuir model were 37.20 and 32.06 mg g−1 for Reactive Red 195 and Methylene Blue, respectively. The pseudo-first-order equation provided the best description for the adsorption kinetics. The evaluated thermodynamic parameters for adsorption indicated that the process was endothermic, random, and spontaneous. These results suggest that the cobalt hydroxide-loaded polystyrene waste could serve as an effective adsorbent for the removal of dyes from water.

Mesoporous biobased carbonaceous adsorbent for dye removal from water: Eutectic molten salts effect and adsorption mechanisms

Dye-polluted wastewater is released from various industries, such as textile and paint industries. Among different reclamation techniques, adsorption has been widely used for dye removal. Carbonaceous adsorbents, such as graphene, are among the most sought-after compounds for adsorption applications because of their high specific surface area and adjustable surface features. In this study, graphene-like carbon (GLC) was prepared from biomass as it is a facile and eco-friendly approach. Biomass-derived GLC was prepared by pyrolyzing waste wood in the presence of FeCl3/ZnCl2 as a eutectic binary mixture. Brunauer–Emmett–Teller (BET) and Raman analyses revealed that FeCl3 had a template effect during pyrolysis, whereas ZnCl2 acted as a pore former. Moreover, FeCl3 and ZnCl2 concentrations positively affected the BET value, regardless of the salt type. Further, waste wood-derived graphene-like carbon (WGLC) pyrolyzed at 900 °C with biomass: FeCl3: ZnCl2 at a ratio of 1:2:1 (WGLC-121) showed the highest specific surface area (2073.78 m2 g−1) and could remove >90 % of rhodamine B (RhB) and Congo red (CR) dyes. The pseudo-second order kinetic model showed a stronger correlation with the experimental data than the pseudo-first order model. While intra-particle diffusion was the rate-determining step in RhB adsorption, it did not influence CR adsorption. Further, the Freundlich model better explained the RhB (qmax = 633.86 mg g−1) and CR (qmax = 141.28 mg g−1) adsorption and revealed the superiority of WGLC-121 in dye removal compared to the previously reported adsorbents. The adsorption isotherm, energy, and thermodynamic parameters confirmed that the dyes were adsorbed through physisorption. Furthermore, the inter-molecular interaction between the RhB and CR molecules influenced the dye adsorption rate and isotherm. The findings of this study demonstrate the high potential of a binary mixture of FeCl3 and ZnCl2 for preparing carbonaceous adsorbents from waste wood to remove dyes from industrial wastewater.

Sonocrystallization of a novel ZIF/zeolite composite adsorbent with high chemical stability for removal of the pharmaceutical pollutant azithromycin from contaminated water

Water pollution management, reduction, and elimination are critical challenges of the current era that threaten millions of lives. By spreading the coronavirus in December 2019, the use of antibiotics, such as azithromycin increased. This drug was not metabolized, and entered the surface waters. ZIF-8/Zeolit composite was made by the sonochemical method. Furthermore, the effect of pH, the regeneration of adsorbents, kinetics, isotherms, and thermodynamics were attended. The adsorption capacity of zeolite, ZIF-8, and the composite ZIF-8/Zeolite were 22.37, 235.3, and 131 mg/g, respectively. The adsorbent reaches the equilibrium in 60 min, and at pH = 8. The adsorption process was spontaneous, endothermic associated with increased entropy. The results of the experiment were analyzed using Langmuir isotherms and pseudo-second order kinetic models with a R2 of 0.99, and successfully removing the composite by 85% in 10 cycles. It indicated that the maximum amount of drug could be removed with a small amount of composite.

Ciprofloxacin Removal Using Pillared Clays

In this work, Ti-pillared bentonites were evaluated to remove ciprofloxacin (CIP) from the aqueous solution. Pillared sodium bentonite (BSP) and pillared calcium bentonite (BCP) were prepared by means of the sol–gel method using titanium tetraisopropoxide with calcination for 3 h at 500 °C. They were characterized using the BET method for N2 adsorption, and subjected to X-ray diffraction and Fourier transform infrared spectroscopy. The results show that the surface area of the pillared bentonites increased after the process, more than the natural ones. Pillared sodium bentonite has a more porous structure, larger surface areas, and higher adsorption capacity than pillared calcium bentonite. The kinetic adsorption of ciprofloxacin (CIP) onto pillared bentonites is well described by the pseudo second-order kinetic model. The BSP isotherm well fitted the Freundlich model, while the BCP isotherm fits the BET model better, suggesting multilayer adsorption. DR model shows mostly physical adsorption for CIP on the two adsorbents. The pH influence study indicated that CIP is adsorbed at pH between 6 and 8, which facilitates the use of BCP and BSP in wastewater treatment, whose pH generally oscillates between these ranges.

Adsorptive removal of 4-hydroxybenzoic acid via cross-linked polymeric microbeads: analysis of isothermal, kinetic and thermodynamic parameters

In this study, the performance of cross-linked microbeads prepared through suspension polymerization was investigated for removal of 4-hydroxybenzoic acid (4-HBA) from aqueous solution. Adsorption studies were conducted at different pHs (2.0–8.0), temperatures (282–308 K) and initial 4-HBA concentrations (1–500 mg/L). The maximum 4-HBA adsorption was 49.05 ± 2.89 mg/g at pH 2.0 (282 K). The adsorption data obeyed to the Langmuir isotherm model. The modified Ritchie second-order and the pseudo second-order kinetic model fitted the adsorption data. The 4-HBA adsorption capacity did not significantly change after 10 consecutive usages. Gibbs free energy changes of the adsorption were calculated as −24.372, −28.431 and −29.093 kJ/mol for 282, 298 and 308 K, respectively. The microbeads were also used for the removal of 4-HBA from spiked river water samples. The removal efficiencies of 43.2% to 68.8% and RSDs of 0.49% to 4.78% demonstrated the usability of the microbeads in application.

Synthesis of a micro-nano FeOx/MnOx modified large volume non-enamel ceramsites for selective and efficient adsorption of cadmium

The synthesis of large volume ceramsites with clay minerals for Cd(II) removal has received extensive attention. Here, micro-nano iron oxides (FeOx) and manganese oxides (MnOx) modified non-enamel ceramsites (NCs) were applied for the selective adsorption of Cd(II) from wastewater. The response surface regression model was exploited to fit the adsorption data, and the results manifested that kaolin/palygorskite (KP):microporous-forming material (MM):bonding material (BM) = 100.0:8.3:12.8 at 555 ℃ obtained the optimal adsorption ability. Furthermore, the Cd(II) adsorption was better accordance with Freundlich and pseudo-second order kinetics models, and FeOx/MnOx-NCs and MnOx-NCs showed maximum adsorption capacity of 6.92 mg/g and 10.36 mg/g at pH 6.0, were 4.7 and 7.4 times higher than that of NCs, respectively. The analyses of Zeta potential, XRD and XPS pointed out that electrostatic attraction, surface chemical complexation with oxygen-containing functional groups and chemical precipitation were the dominant adsorption mechanisms. The FeOx/MnOx-NCs and MnOx-NCs retained their excellent removal rates (96.31% and 97.78%, respectively) for Cd(II) in the coexistence of salt cations. Moreover, high regeneration ability for both adsorbents were observed for five consecutive adsorption-desorption cycles. Therefore, this work provides new insight for producing large volume ceramsites using environment-friendly clay, which can overcome the constraints of selective adsorption of heavy metals and convert available ceramsites into a recyclable resource.

Assessment on the photocatalytic and phytotoxic activities using ecobenevolently synthesized iron oxide nanoparticles from the root extracts of Glycyrrhiza glabra.

The present study is the first attempt to utilize the root extracts of Glycyrrhiza glabra as a novel biological route for the synthesis of iron oxide nanoparticles (Fe2O3NPs) under optimized conditions. The process variables namely concentration of ferric chloride, root extract ofG. glabra and temperature were optimized using Response Surface Methodology (RSM) to obtain high yield. Phytochemicals mediated the reduction process and served as capping and stabilizing agent. The biosynthesized Fe2O3NPs characterized using UV-Vis spectroscopy exhibited a prominent peak at 350nm. The crystallinity and valence state of Fe2O3NPs was confirmed by XRD and XPS. The surface functionalization of the nanoparticles was confirmed from the presence of functional groups in the FT-IR spectrum. The FESEM analysis revealed the biosynthesized Fe2O3NPs are irregular and the EDX spectrum recorded the presence of iron and oxygen in the synthesized nanoparticles. The biosynthesized Fe2O3NPs exhibited an appreciable photocatalytic activity against methylene blue under sunlight with a maximum decolorisation efficiency of 92% within 180min of reaction time. The experimental data of adsorption studies well fitted with Langmuir isotherm and pseudo-second order kinetic model. The thermodynamic study proved to be spontaneous, feasible and endothermic in nature. The phytotoxicity study revealed 92% germination and increased seedling growth in the green gram seeds exposed to Fe2O3NPs. Hence the study established the efficiency of biosynthesized of Fe2O3NPs in photocatalytic and phytotoxic activities.

Efficient removal of Mn2+ ions from aqueous solutions using apple pomace biochar

The increasing contamination of water resources is a severe environmental problem. Manganese is highly soluble in water, has adverse effects on the environment and human health during excessive exposure, and is difficult to remove. Biosorbents have been suggested to remove metals from aqueous solutions, therefore, apple pomace was utilized to prepare activated biochar (activated charcoal from apple pomace, ACAP). The biochar sample was characterized by X-ray fluorescence spectrometry, scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and Brunauer–Emmett–Teller analysis. The aim of this study was to use ACAP as an adsorbent to remove Mn2+ ions from aqueous solutions. Adsorption experiments were performed in the pH range 3.2–6.5, with various masses of ACAP biochar and Mn2+ ion concentrations. The results were evaluated using the pseudo-first order, pseudo-second order, general order, Elovich, and Webber and Morris kinetics models. All the models fitted the experimental results, the equilibrium time was 15 min, and the pseudo-second order model presented the highest constant (k2), indicating that chemosorption is an important mechanism in adsorption. The adsorption isotherm results were adjusted using different models, wherein the Langmuir and Temkin models exhibited the best fit to the experimental results. Adsorption experiments yielded a 97.5% removal rate of Mn2+ ions at pH 6.5 and <5% at pH 3.2, and the desorption of manganese in nitric acid (0.1 M) was 97.5%. Overall, apple pomace biochar is an efficient adsorbent for removing Mn2+ ions in aqueous media, and is applicable for treating water for human consumption.

Removal of methylene blue from aqueous solution by adsorption onto hydroxyapatite nanoparticles

Water pollution due to industrial discharges is a major problem in many countries as it can have adverse effects on the environment and human health. Among wastewater treatment processes, adsorption technique is widely used to reduce the harmful effects of many pollutants, including dyes. The main objective of this research is to characterize and evaluate the removal capacity of methylene blue (a cationic dye) from an aqueous solution using hydroxyapatite as a bio-adsorbent. Hydroxyapatite was prepared by two different methods and the resulting biomaterials were designated HAp A, HAp B, HAp C, and HAp D. A comparative study of methylene blue adsorption by these biomaterials was performed. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to characterize these adsorbents. The effects of various experimental parameters such as contact time (5–120 min), concentration (5–90 mg/L), pH (6–12) and temperature (25–6°C) were studied. Adsorption studies revealed a removal efficiency of 88.88% at an initial MB concentration of 45 mg/L, an equilibrium time of 20 min, Basic pH and a temperature of 25 °C. The pseudo-second order kinetic model was used to describe the adsorption kinetics, while the Freundlich adsorption isotherm was used to describe the equilibrium adsorption process. This research suggests that the method of synthesis has a significant impact on the ability of the adsorbent to remove organic pollutants from dyes in an aqueous solution.

Performance of first derivative UV/Visible spectra for kinetic and isothermal study of simultaneous adsorption of o-nitrophenol and p-nitrophenol onto Al2O3 and HDTMA+/Al2O3 composite

Adsorption of ortho-nitrophenol (o-NP) and para-nitrophenol (p-NP) from single and binary aqueous solutions onto Al2O3 and its composite, hexadecyltrimethylammonium bromide (HDTMA+/Al2O3), were studied in batch experiments at T = 25 °C and at pH = 6. In order to overcome the problem of overlapping absorbance bands of o-NP and p-NP, a first-order derivative UV/Visible spectrophotometric method (FODS) was applied for the simultaneous determination of each adsorbate in their residual binary solutions. Experimental adsorption data of o-NP and p-NP in single and binary solutions were found to follow adequately a pseudo-second order kinetic model. Based on the values of R2, χ2 and Δq(%), the Freundlich model showed better fitting to the equilibrium isotherms data, followed by Redlich-Peterson and Langmuir models, suggesting the existence of heterogeneous sites on the adsorbent surfaces. In all the experiments, HDTMA+/Al2O3 showed a superior adsorption capacity for o-NP and p-NP than Al2O3, and the adsorption of o-NP on both adsorbents was favored. However, adsorption capacity of each isomer in binary mixtures were found lower than that in a single component, reflecting a competitive adsorption mechanism, involving mainly the hydrogen bonding between NO2 and OH groups of o-NP/p-NP and the functional groups of the adsorbents, which affected their selectivity.

Fe3O4 imbuing carboxymethyl cellulose/dextran sulfate nanocomposite hydrogel beads: an effective adsorbent for methylene blue dye pollutant

In this study, initially synthesized magnetic nanoparticles modified with citrate ions (MNPs/m-MNPs) were entrapped in aluminum-carboxymethyl cellulose/dextran sulfate beads to form hybrid nanocomposites (m-MNPs-C/D0.5) using a simple two-pot method. Sodium dodecyl sulfate surfactant was employed to develop a porous interconnected structure. The synergistic effect of the hybrid nanocomposites was studied for the parametric adsorption of methylene blue dye pollutant. The swelling ability of hybrid hydrogels was also studied for different solution pH. The results clearly indicated that equilibrium was reached faster at about 3 h for the m-MNPs-loaded magnetic beads (m-MNPs-C/D0.5), whereas at 6 h for the MNPs-loaded beads (MNPs0.4-C/D0.5) and the unloaded simple ones (MNPs0-C/D0.5). Experimental data modeling of adsorption kinetics and isotherms as well as thermodynamic study showed a good correlation with pseudo-second order kinetic and Langmuir models while the adsorption process on magnetic beads was exothermic. The maximum adsorption capacity for MNPs0-C/D0.5 and the optimized m-MNPs0.3-C/D0.5 hydrogel were 380 and 529 mg g−1, respectively. Furthermore, all hydrogels were perfectly regenerated and then reused for five adsorption-desorption cycles without apparent loss of stability that confirms their consideration as alternative and effective adsorbents for wastewater treatment. The manufactured beads were characterized by scanning electron microscopy/energy dispersive X-Ray, dynamic light scattering, X-ray diffraction, thermogravimetric analysis, vibrating sample magnetometer and fourier-transform infrared spectroscopy.

Adsorption of Zn2+ ion by macadamia nut shell biochar modified with carboxymethyl chitosan and potassium ferrate

A series of biochars and modified biochars were prepared by using macadamia nut shell (MNS) as raw material at different calcination temperatures and further using carboxymethyl chitosan (CMC) and K2FeO4 as the modifying agent, respectively. These biochar and modified biochars were used as adsorbents for adsorbing Zn2+ ion in aqueous solution. It is found that the adsorption behaviors of modified biochars BC-CMC and BC-K2FeO4 are consistent to the pseudo second-order kinetics model and the Langmuir equation. The maximum adsorption capacities for these adsorbents are increased in the following order: BC-CMC > BC-K2FeO4 > > BC-700. Among these biochars, BC-CMC exhibits the highest adsorption capacity of 97.09 mg/g, which may be mainly due to that BC-CMC has more amino, hydroxyl and carboxyl functional groups. The BC-CMC also exhibits better desorption performance and reusability. Furthermore, BC-CMC also shows higher adsorption capacity for Cu2+ and Pb2+. Based on the results, the adsorption mechanism of BC-CMC for Zn2+ was also proposed.

Impact of modification on the properties of Eucheuma biochar and its adsorption of phenanthrene from aqueous solution

Biochar was derived from Eucheuma (EBC) at a temperature of 500 °C and the resulting biochar was modified using NaOH, KOH, NaOH + KOH and HNO3 + HCl. This study investigated the impact of these modifications on the characteristics of the biochar and its effectiveness in adsorbing phenanthrene (Phe) from an aqueous solution. The results indicated that the surface roughness increased, leading to an increase in the specific surface area, and the development of complex pore structure, leading to a decrease in the polarity and increase in hydrophobicity of biochar modified by a mixture of KOH and HNO3 + HCl (EBC-K and EBC-H). The EBC-K and EBC-H samples exhibited superior surface areas (272.76 and 289.60 m2 g−1) and adsorption capabilities for Phe (removal rates of 99.8% and 99.4%). The pseudo-first order, pseudo-second order and intraparticle diffusion Kinetic model demonstrated that the adsorption process is determined by both physicochemical and intra-particle diffusion. The adsorption process was well described by the Langmuir model. The maximum adsorption capacity of EBC-K and EBC-H was increased by approximately 2.4 times compared with the original biochar. Batch adsorption experiments indicated that the removal rate increases with the increase of dosage. Additionally, EBC-H regenerated from n-hexane removed 85.52% of the Phe solution.

Adsorption Mechanism for Phosphate in Aqueous Solutions of Calcium/Aluminum-rich Sludge Biochar Composite

Excess sludge is rich in organic matter but also contains heavy metals, pathogens, and harmful substances. In this study, hydroaluminite and excess sludge were used as raw materials to reduce the risk of heavy metals leaching from sludge by coagulation and co-pyrolysis, and its phosphate adsorption characteristics were studied. The results showed that the leaching amount of Zn, Cu, Cd, and Ni in sludge biochar decreased with the increase in the hydroaluminite dosage. The sludge biochar composite (1:1HB800), prepared by co-pyrolysis of hydroaluminite and excess sludge with a mass ratio of 1:1 as well as rich in calcium and aluminum, had lowest leaching risk of heavy metals and showed the high adsorption capacity for phosphate. The process could be fitted by the Langmuir adsorption isotherm (R2=0.93), and the maximum phosphate adsorption capacity at 25℃ was 51.38 mg·g-1. The pseudo second-order kinetic model could well describe the adsorption process of 1:1HB800 for high concentration phosphate, and its adsorption rate was controlled by both surface adsorption and particle diffusion. Compared with that in the neutral solution, 1:1HB800 had better phosphate capacity in the acidic and alkaline aqueous solutions, which was related to the leaching amount of calcium/aluminum in 1:1HB800 and the existence form of aluminum under the different pH conditions. FTIR, XRD, SEM, zero potential point, and Ca2+/Al3+ leaching experiments indicated that the main adsorption mechanisms for phosphate by 1:1HB800 were co-precipitation (interaction between Ca2+/Al3+ and phosphate), ligand exchange (hydroxyl), and electrostatic interaction. Therefore, 1:1HB800 can provide a feasible alternative for the removal of phosphate in aqueous solutions and also provide a potential new method for the resource utilization and harmless treatment of excess sludge.

Plantain peel adsorbent: Simple preparation, and adsorption at phosphate concentrations similar to those of water sources at risk of eutrophication

There are several investigations on the use of food waste to remove contaminants by adsorption. However, a simple route, without chemical activation reagents, is needed for the development of adsorbents. The aim of this study was to develop an adsorbent from plantain peel, using a simple procedure, and to evaluate its capacity to remove phosphate from aqueous solutions at phosphate concentrations similar to those of water sources at risk of eutrophication (0.30 mg/L). The simple pyrolysis method was used in an electric muffle, without chemical activation, using plantain peel as precursor. The variables evaluated were pyrolysis temperature and solution pH. The specific surface area BET, zero loading point of the developed treatments, was determined. Phosphate adsorption was studied in a batch experiment in the presence of calcium ions in solution. Phosphate adsorption was favorable at all three pyrolysis temperature levels (500, 600 and 700 °C) and two solution pH levels (pH 7 and 10). the pseudo-second order kinetic model was the best fit for the experimental data to describe the adsorption mechanism. The best fit to the experimental equilibrium data was obtained with the Langmuir isotherm model. It was found that a 1 g/L dose of the adsorbent was able to reduce 92% of phosphate in water, with a removal capacity 0.14 mg/g at pH 10 and pyrolysis temperature of 700 °C. This study lays the groundwork for future research on the use of this type of adsorbent in water treatment to facilitate access to clean water for rural populations.