Single and competitive adsorption affinity of heavy metals toward peanut shell-derived biochar and its mechanisms in aqueous systems

Converting peanut shells into biochar by pyrolysis was considered an environmentally friendly and efficient method for agricultural solid waste disposal.The properties of peanut shell-derived biochar(PBC)under different temperature and its adsorption capacity of heavy metals were investigated.It was found that PBC400 exhibited the highest cumulative capability for heavy metals elimination in single solute because of its high specific surface area and rich functional groups.Furthermore,the competitive adsorption revealed that PBC had a substantial difference in adsorption affinity from diverse heavy metal ions,sorption capacity decreased as Pb2+>Cu2+>Cd2+>Ni2+>Zn2+,which was lower than in a single solute.The adsorption process using selected biochar was optimized with respect to p H,reaction time,adsorbent dose,and initial concentration of heavy metals.The kinetic data was well fitted with PSO model,and the Langmuir model was adopted for adsorption equilibrium data in both cases of single solutes and mixed solutes for all heavy metals,which indicated that the removal course was primarily explained by monolayer adsorption,and chemical adsorption occupied an important role.Therefore,peanut shells derived biochar could be a potential and green adsorbent for wastewater treatment.

Binary competitive adsorption of naphthalene compounds onto an aminated hypercrosslinked macroporous polymeric adsorbent

An aminated hypercrosslinked macroporous polymeric adsorbent was synthesized and characterized. Adsorption isotherms for 1 amino 2 naphthol 4 sulfonic acid(1, 2, 4 acid) and 2 naphthol obtained from various binary adsorption environments can be well fitted by Freundlich equation, which indicated a favorable adsorption process in the studied range. Adsorption for 1, 2, 4 acid was an endothermic process in comparison with that for 2 naphthol of an exothermic process. 2 naphthol molecules put a little influence on the adsorption capacity for 1, 2, 4 acid. However, the adsorption to 1, 2, 4 acid depressed that to 2 naphthol in a large extent for the stronger electrostatic interaction between 1, 2, 4 acid and adsorbent. The predominant mechanism can be contributed to the competition for adsorption sites. And the simultaneous environment was confirmed to be helpful to the selective adsorption towards 1,2,4 acid based on the larger selectivity index.

Effect of Competitive Adsorption between Sodium Tripolyphosphate and Naphthalene Superplasticizer on Fluidity of Cement Paste

The adsorption amount, ξ-potential of cement particles and fluidity of cement paste were tested to research the competitive adsorption between naphthalene superplasticizer （FDN） and STPP. The experimental results showed that the presence of STPP could significantly improve the fluidity of cement paste and reduce the fluidity loss with FDN. There existed a competitive adsorption between STPP and FDN. STPP and calcium ions formed complexes; they preferentially adsorbed onto surface of cement particles and preempt adsorption points of FDN; and it reduced adsorption amount of FDN. In the absence of STPP, saturation adsorption amount of FDN was 5.93 mg/g; but when the dosage of STPP was 0.1%, it reduced to 4.3 mg/g （about 72.5%）. The adsorption amount of FDN was reduced by STPP, but ξ-potential of cement particles enhanced and fluidity of cement paste increased because of strong negative charge effect of the complexes. Adsorption of the complexes would delay Ca^2＋ into liquid and inhibit formation of active adsorption points. Then, content of FDN in liquid increased with the addition of STPP and ξ-potential of cement particles became stable. In this way, fluidity loss of cement paste reduced.

A New Competitive Adsorption Isothermal Model of Heavy Metals in Soils

A new competitive adsorption isothermal model(CAIM)was developed for the coexistent and competitive binding of heavy metals to the soil surface.This model extended the earlier adsorption isothermal models by considering more than one kind of ion adsorption on the soil surface.It was compared with the Langmuir model using different conditions, and it was found that CAIM,which was suitable for competitive ion adsorption at the soil solid-liquid surface,had more advantages than the Langmuir model.The new competitive adsorption isothermal model was used to fit the data of heavy metal(Zn and Cd)competitive adsorption by a yellow soil at two temperatures.The results showed that CAIM was appropriate for the competitive adsorption of heavy metals on the soil surface at different temperatures.The fitted parameters of CAIM had explicit physical meaning.The model allowed for the calculation of the standard molar Gibbs free energy change,the standard molar enthalpy change,and the standard molar entropy change of the competitive adsorption of the heavy metals,Zn and Cd,by the yellow soil at two temperatures using the thermodynamic equilibrium constants.

Competitive adsorption of heavy metal ions on peat

The uptake capacities, and the adsorption kinetics, of copper, Cu（Ⅱ）, nickel, Ni（Ⅱ）, and cadmium, Cd（Ⅱ）, on peat have been studied under static conditions. The results show that the adsorption rates are rapid： equilibrium is reached in twenty minutes. The adsorption of copper, nickel and cadmium is pH dependent over the pH range from 2 to 6. The adsorption kinetics can be excellently described by the Elovich kinetic equation. The adsorption isotherm fits a Langmuir model very well. The adsorption capacities follow the order Cu^2＋ 〉 Ni^2＋〉 Cd^2＋ in single-component systems and the competitive adsorption capacities fall in the decreasing order Cu^2＋ 〉 Ni^2＋〉 Cd^2＋ in multi-component systems. The adsorption capacities of these three heavy metal ions on peat are consistent with their observed competitive adsorption capacities.

Preparation of Fe3O4-octadecyltrichlorosilane for Removal of Methyl Orange and Methylene Blue:Influence of p H and Ionic Strength on Competitive Adsorption

Fe3O4-octadecyltrichlorosilane（Fe3O4-OTS）was synthesized and used to remove dyes in a competitive system.Fe3O4-OTS was prepared by slow hydrolysis of OTS in cyclohexane on the surface of Fe3O4obtained through coprecipitation method.Scanning electron microscope（SEM）,energy dispersive spectrometer（EDS）,and contact angle analyzer（CA）were used to analyze the properties of Fe3O4-OTS.Methyl orange（MO）and methylene blue（MB）were selected as model molecules to study the influence mechanism of p H and ionic strength on competitive adsorption.The results of EDS and CA indicated that Fe3O4 was modified successfully with OTS on the surface.Silicon appeared and carbon content increased obviously on the surface of adsorbent.Contact angle of adsorbent increased from 0~o to 107~o after being modified by OTS.Fe3O4-OTS showed good separation for MO and MB in competitive system,which has potential to separate dyes in sewage.Separation factor（β~OB）changed from 18.724 to 0.017,when p H changed from 7 to 12,revealing that MO and MB could be separated almost thoroughly by Fe3O4-OTS.p H could change the surface charge of Fe3O4-OTS and structure of dyes,and thus change the interactions of competitive system indirectly.Even though hydrophobic interaction was enhanced,ionic strength reduced the difference of electrostatic interaction between dyes and Fe3O4-OTS.So it is unfavorable to separate dyes with opposite charges when ionic strength increases.These findings may provide theoretical guidances to separate two-component dye pollutants.

Competitive adsorption of Cu(II) and Pb(II) ions from aqueous solutions by Ca-alginate immobilized activated carbon and Saccharomyces cerevisiae

To establish a theoretical foundation for simultaneous removal of multi-heavy metals,the adsorption of Cu（Ⅱ） and Pb（Ⅱ） ions from their single and binary systems by Ca-alginate immobilized activated carbon and Saccharomyces cerevisiae （CAS） was investigated.The CAS beads were characterized by Scanning electron microscope （SEM） and Fourier transformed infrared spectroscopy （FTTR）.The effect of initial pH,adsorbent dosage,contact time and initial metal ions concentration on the adsorption process was systematically investigated.The experimental maximum contents of Cu（Ⅱ） and Pb（Ⅱ） uptake capacity were determined as 64.90 and 166.31 mg/g,respectively.The pseudo-second-order rate equation and Langmuir isotherm model could explain respectively the kinetic and isotherm experimental data of Cu（Ⅱ） and Pb（Ⅱ） ions in single-component systems with much satisfaction.The experimental adsorption data of Cu（Ⅱ） and Pb（Ⅱ） ions in binary system were best described by the extended Freundlich isotherm and the extended Langmuir isotherm,respectively.The removal of Cu（lⅡ） ions was more significantly influenced by the presence of the coexistent Pb（Ⅱ） species,while the Pb（Ⅱ） removal was affected slightly by varying the initial concentration of Cu（Ⅱ）.The CAS was successfully regenerated using 1 mol/L HNO3 solution.

Competitive adsorption and mobility sequence of heavy metals in urban soils of southeastern China

Heavy metals can be introduced into urban soils at the same time. Therefore, their selective retention and competitive adsorption by the soils become of major importance in determining their availability and movement throughout the soil. In this study, the availability and mobility of six heavy metals in eight urban soils collected from different cities of Zhejiang Province, southeastern China were assessed using distribution coefficients（Kd） and retardation factor（Rf）. The results showed that there were great differences in the Kd and Rfamong the tested soils. The adsorption sequences were Cr〉Pb〉Cu〉Cd〉Zn〉Ni, and the Kd decreased with increasing levels of metal addition. Ni generally has the lowest Rf values followed closely by Cd, and Zn whereas Cr and Pb reached the highest values. The results suggest that Ni and Zn have the highest mobility associated to the lowest adsorption, Cr and Pb present the opposite behavior. Correlation analysis indicates that soil pH, CaCO3 content, and cation exchange capacity （CEC） are key factors controlling the solubility and mobility of the metals in the urban soils.

Competitive adsorption of Cd, Cu, Hg and Pb by agricultural soils of the Changjiang and Zhujiang deltas in China

Soils can often be contaminated simultaneously by more than one heavy metal. The sorption-desorption behavior of a metal in a soil will be affected by the presence of other metals. Therefore, selective retention and competitive adsorption of the soils to heavy metals can affect their availability and movement through the soils. In this study, the simultaneous competitive adsorption of four heavy metals (Cd, Cu, Hg, and Pb) on ten agricultural soils collected from the Changjiang and Zhujiang deltas, China was assessed. The results showed that the competition affected the behavior of heavy metal cations in such a way that the soils adsorbed less Cd and Hg, and more Pb and Cu with increasing total metal concentrations, regardless of the molar concen- tration applied. As the applied concentrations increased, Pb and Cu adsorption increased, while Cd and Hg adsorption decreased. The adsorption sequence most found was Pb>Cu>Hg>Cd. The maximum adsorption capacity for the heavy metal cations was calculated, and affected markedly by soil properties. The results suggest that Hg and Cd have higher mobility associated to the lower adsorption and that Pb and Cu present the opposite behavior. Significant correlations were found between the maximum adsorption capacity of the metals and pH value and exchangeable acid, suggesting that soil pH and exchangeable acid were key factors controlling the solubility and mobility of the metals in the agricultural soils.

Kinetics comparison on simultaneous and sequential competitive adsorption of heavy metals in red soils

To compare the adsorption kinetics of Cu, Zn and Cd introduced into red soils simultaneously and sequentially as well as their distribution coefficients, the ability of red soils to retain heavy metals was evaluated by performing batch experiments. The results indicate that Cu is preferentially adsorbed by red soils no matter in simultaneous or in sequential situation. The adsorption amount of Cd is the minimum in simultaneous competitive adsorption experiment. As heavy metals are added into red soils sequentially, the heavy metal adsorptions are relatively hard to reach equilibrium in 2 h. Red soils retain more Cd than Zn, which is opposite to the result in simultaneous adsorption. The addition sequences of heavy metals affect their adsorbed amounts in red soils to a certain extent. The joint distribution coefficients of metals in simultaneous adsorption are slightly higher than those in sequential adsorption.

Mechanism transformation of cyclohexene-thiophene competitive adsorption in FAU zeolite

Competition of hydrocarbon compounds with sulfides in gasoline has caused a not very high selectivity of sulfides in adsorption desulfurization so far,resulting in a reduction of catalyst lifetime as well as more sulfur oxide emissions.Tostudy the whole competitive process changing with the increase of the loading,the dynamic competition adsorption mechanism of cyclohexene and thiophene in siliceous faujasite(FAU)zeolite was analyzed by the Monte Carlo simulation.The results showed that with the increase of the loading,thiophene and cyclohexene had different performances before and after the inflection point of 40 molecule/UC.The adsorbates were distributed ideally at optimal sites during the stage that occurred before the inflection point,which is called the“optimal-displacement adsorption”stage.When approaching the inflection point,the competition became apparent and the displacement appeared accordingly,some thiophene molecules at S sites(refers to the sites inside the supercages)were displaced by cyclohexene.After the inflection point,the concentration of adsorbates at W sites(refers to the 12-membered ring connecting the supercages)was significantly reduced,whereas the adsorbates at S sites got more concentrated.The stage some cyclohexene molecules displaced by thiophene and inserted into the center of the supercage can be named as the“insertion-displacement adsorption”stage,and both the adsorption behavior and the competitive relationship became localized when the adsorption amount became saturated.This shift in the competitive adsorption mechanism was due to the sharp increase of interaction energy between the adsorbates.Besides,the increase in temperature and ratio of Si/Al will allow the adsorbates,especially thiophene molecules to occupy more adsorption sites,and it is beneficial to improve the desulfurization selectivity.

Competitive Adsorption between Bovine Serum Albumin and Collagen Observed by Atomic Force Microscope

Atomic force microscopy (AFM) was used to study the competitive adsorption betweenbovine serum albumin (BSA) and type Ⅰ collagen on hydrophilic and hydrophobic silicon wafers.BSA showed a grain shape and the type Ⅰ collagen displayed fibril-like molecules with relativelyhomogeneous height and width, characterized with clear twisting (helical formation). These AFMimages illustrated that quite a lot of type Ⅰ collagen appeared in the adsorption layer on hydrophilicsurface in a competitive adsorption state, but the adsorption of BSA was more preponderant than thatof type Ⅰ collagen on hydrophobic silicon wafer surface. The experiments showed that theinfluence of BSA on type Ⅰ collagen adsorption on hydrophilic surface was less than that onhydrophobic surface.

The Competitive Adsorption Characteristics of Welan Gum and Superplasticizer in Cement Mortar

Welan gum has been widely used in oil cement and grouting materials for its excellent rheological properties and anti-bleeding,and most of all,being friendly to the environment.However,when welan gum was added,the fluidity of mortar decreased sharply,so it should be used together with a superplasticizer to enable good workability.With its powerful charge density in the molecular structure,the competitive adsorption between welan gum and other admixtures happened remarkably during the addition process.Consequently,we experimentally studied on the bleeding rate and rheological properties of cement slurry,fluidity and mechanical properties of mortar with welan gum mixed with superplasticizer,aiming at understanding the competitive adsorption phenomenon by application of welan gum mixed with superplasticizer.By measuring the hydration heat and zeta potential,the mechanism of interaction of welan gum with superplasticizer was deduced and explained.The results showed that it could ensure a good dispersion effect when welan gum is mixed with the two kinds of superplasticizer.Welan gum had little impact on the naphthalene superplasticizer,but did have a substantial influence on polycarboxylate.In practice,adding welan gum after PCE acted with cement for 2 min could effectively avoid the competitive adsorption and then achieve better performance.On this viewpoint for mortar with PCE,new delay release welan gum needs further research and development.

STUDIES ON THE DYNAMIC COMPETITIVE ADSORPTION OF ORGANIC VAPORS ON THE ACTIVATED CARBON FIBERS ACTIVATED WITH PHOSPHORIC ACID

The dynamic competitive adsorption behaviors of different binary organic vapor mixtures on ACF-Ps under different operation conditions were investigated by gas chromatography in this paper. The studied mixtures included benzene/toluene, toluene/xylene, benzene/isopropylbenzene, ethyl acetate/toluene and benzene/ethyl acetate. Experimental results show that various ACF-Ps, as with ACF-W, can remove both vapors in binary vapor mixtures with over 99% of removal efficiency before the breakthrough point of the more weakly adsorbed vapor. In dynamic competitive adsorption, the more weakly adsorbed vapor not only penetrates early, but also will be displaced and desorbed consequently by stronger adsorbate and therefore produces a rolling up in the breakthrough curve. The ACF-Ps prepared at different temperatures have somewhat different adsorption selectivity. The feed concentration ratio of vapors, the length/diameter ratio and the thick of bed have effect on competitive adsorption. The competitive adsorption ability of a vapor is mainly related to its boiling point. Usually, the higher the boiling point, the stronger the vapor adsorbed on ACF-P.

Competitive adsorption and desorption of copper and lead in some soil of North China

The competitive adsorption and desorption of Pb（II） and Cu（II） ions in the soil of three sites in North China were investigated using single and binary metal solutions with 0.01 tool. L^-1 CaC12 as background electrolyte. The desorption isotherms of Pb（lI） and Cu（II） were similar to the adsorption isotherms, which can be fitted well by Freundlich equation （R2 〉 0.96）. The soil in the three sites had greater sorption capacities for Pb（II） than Cu （II）, which was affected strongly by the soil characteristics. In the binary metal solution containing 1 ： 1 molar ratio of Pb（II） and Cu（II）, the total amount of Pb（II） and Cu（lI） adsorption was affected by the simultaneous presence of the two metal ions, indicating the existence of adsorption competition between the two metal ions. Fourier transform infrared （FT-IR） spectroscopy was used to investigate the interaction between soil and metal ions, and the results revealed that the carboxyl and hydroxyl groups in the soil were the main binding sites of metal ions.

Study of CH_(4)and CO_(2)competitive adsorption on shale in Yibin,Sichuan Province of China

Shale gas is an unconventional gas source with substantial development potential.In this study,Longmaxi Formation shale from the Silurian system in Yibin,Sichuan Province was collected for characterizing total organic carbon(TOC),clay mineral content,and other reservoir properties.The pore structure of shale was analyzed by field-emission scanning electron microscopy and low-temperature N_(2) adsorption–desorption method.Isothermal adsorption experiments for CH_(4)and CO_(2)mixtures in shale samples were performed.The second Virial coefficient was used to calculate for the compressibility factor of the gas mixture.The influencing factors of gas adsorption capacity of shale were analyzed.Finally,the CH_(4)and CO_(2)adsorption capacities and selection of shale samples were investigated.Under low pressure,the total gas mixture capacity of shale samples was positively correlated with pressure.When the pressure increased to a certain extent,the growth trend of gas mixture adsorption capacity of shale samples decreased.The mixed gas adsorption volume is high at 50℃ for all the proportion.Given the same temperature and pressure,the CO_(2)adsorption of shale samples is higher than the CH_(4)adsorption.In competitive adsorption,shale prefers to adsorb CO_(2).Therefore,CO_(2)is easier to be adsorbed by shale and this causes CH_(4)to be released from the adsorption site.

Competitive and cooperative adsorption behaviors of phenol and aniline onto nonpolar macroreticular adsorbents

The adsorption behaviors of phenol and aniline on nonpolar macroreticular adsorbents(NDA100 and Amberlite XAD4) were investigated in single or binary batch system at 293K and 313K respectively in this study. The results indicated that the adsorption isotherms of phenol and aniline on both adsorbents in both systems fitted well Langmuir equation, which indicated a favourable and exothermic process. At the lower equilibrium concentrations, the individual amount adsorbed of phenol or aniline on macroreticular adsorbents in single-component systems was higher than those in binary-component systems because of the competition between phenol and aniline towards the adsorption sites. It is noteworthy, on the contrast, that at higher concentrations, the total uptake amounts of phenol and aniline in binary-component systems were obviously larger than that in single-component systems, and a large excess was noted on the adsorbent surface at saturation, which is presumably due to the cooperative effect primarily arisen from the hydrogen bonding or weak acid-base interaction between phenol and aniline.

BINARY COMPETITIVE AND COOPERATIVE ADSORPTION OF AROMATIC COMPOUNDS ON POLYMERIC RESINS

The adsorption behaviors of 2-naphthalenesulfonic acid and aniline on a conventional macroporous resin Amberlite XAD4 and the other two newly-developed hypercrosslinked resins NDA101 and NDAI00 were investigated in a single or binary batch system at 293 K and 313 K, respectively. All the adsorption isotherms of 2-naphthalenesulfonic acid and aniline on the test resins in both systems can fit well with the Langmuir equation, indicating that the adsorption is a favorable process. At the identical equilibrium concentration, the amount of aniline adsorbed on polymeric resins in the single system is higher than that in the binary system because of the competitive adsorption between 2-naphthalenesulfonic acid and aniline on the resin surface. However, the uptake amount of 2-naphthalenesulfonic acid in the binary system is markedly larger than that in the single system, which is presumably due to the cooperative effect arisen from the electrostatic interaction between 2-naphthalenesulfonic acid and aniline adsorbed on the resin surface. The simultaneous adsorption system was proven to be helpful for the selective adsorption toward 2-naphthalenesulfonic acid due to its larger selective index.

Adsorption and Desorption Characteristics of Cadmium and Lead in Typical Paddy Soils of Jiangxi Province and Its Environmental Risk Assessment

[Objective] This study aimed to investigate the adsorption and desorption characteristics of cadmium and lead in typical paddy soils of Jiangxi Province. [Method] Gleyed paddy soil and waterloggogenic paddy soil were collected from Jiangxi Province and used as experimental materials to investigate single and com- petitive adsorption and desorption behaviors of cadmium and lead by batch equilib- rium method. The environmental risk of the presence of cadmium and lead in paddy soils was assessed using distribution coefficients. [Result] Under equal ratio condi- tions, the adsorption capacity of lead by two types of paddy soils was higher than that of cadmium, and the adsorption rate in waterloggogenic paddy soil was higher than that in gleyed paddy soil. The desorption capacity of cadmium by two types of paddy soils was higher than that of lead, and the desorption rate in gleyed paddy soil was higher than that in waterloggogenic paddy soil. Under competitive condi- tions, the adsorption capacity of cadmium and lead by paddy soils was significantly reduced compared with single ion system, while the desorption rate was remarkably improved. The potential environmental risk of cadmium contamination was greater than that of lead in paddy soils. Moreover, environmental risks of cadmium and lead were reduced with the increase of pH, which increased significantly under the coex- istence state. [Conclusion] In the coexistence of cadmium and lead, cadmium con- tamination should be controlled and avoided compared with lead contamination in paddy soils.

Enhancing the Electrocatalytic Oxidation of 5-Hydroxymethylfurfural Through Cascade Structure Tuning for Highly Stable Biomass Upgrading

Electrocatalytic 5-hydroxymethylfurfural oxidation reaction(HMFOR)provides a promising strategy to convert biomass derivative to highvalue-added chemicals.Herein,a cascade strategy is proposed to construct Pd-NiCo_(2)O_(4)electrocatalyst by Pd loading on Ni-doped Co3O4 and for highly active and stable synergistic HMF oxidation.An elevated current density of 800 mA cm^(-2)can be achieved at 1.5 V,and both Faradaic efficiency and yield of 2,5-furandicarboxylic acid remained close to 100%over 10 consecutive electrolysis.Experimental and theoretical results unveil that the introduction of Pd atoms can modulate the local electronic structure of Ni/Co,which not only balances the competitive adsorption of HMF and OH-species,but also promote the active Ni^(3+)species formation,inducing high indirect oxidation activity.We have also discovered that Ni incorporation facilitates the Co2+pre-oxidation and electrophilic OH*generation to contribute direct oxidation process.This work provides a new approach to design advanced electrocatalyst for biomass upgrading.