pH-dependent Adsorption Research Articles

Detection of arginase through the optical behaviour of liquid crystals due to the pH-dependent adsorption of stearic acid at the aqueous/liquid crystal interface

The authors here developed a stearic acid-doped liquid crystal (LC)-based sensor for the label-free and real-time detection of arginase (ARG1). This sensor was based on the orientational transition of LCs due to the adsorption of stearic acid at the aqueous/LC interface. The shift in the optical image of LCs from bright to dark was obtained after transferring an aqueous solution of arginase, ʟ-arginine, and urease onto the aqueous/stearic acid-doped LC interface. Arginase catalyzes ʟ-arginine hydrolysis to produce urea, which is further catalyzed by urease to produce ammonium, which in turn increases the pH of the aqueous bulk. This increase in pH causes the deprotonation and adsorption of stearic acid and the formation of a stearate self-assembled monolayer at the interface, which induces a change in the orientation of the LC film from planar to homeotropic anchoring. ʟ-norvaline can inhibit the enzymatic activity of arginase; therefore, the LC optical image stayed bright after adding a mixed solution of arginase and ʟ-norvaline to the optical cell incubated with ʟ-arginine and urea, indicating no orientation change of LCs. ARG1 could be quantitatively detected by the proposed sensor in the range from 1 ng/mL to 100 ng/mL, with the detection limit as low as 0.6 ng/mL. The effect of the human serum matrix on the performance of proposed sensors was also investigated to confirm the applicability in ARG1 detection. The proposed sensor shows great potential for the development of pH-sensitive instruments for the monitoring of enzymatic reactions.

A facile method for preparing three-dimensional graphene nanoribbons aerogel for uranium(VI) and thorium(IV) adsorption

An three-dimensional (3D) porous structure graphene oxide nanoribbons (GONRs) aerogel has been prepared via hydrothermal method to overcome the challenges of solid–liquid separation for powdered carbon-based nanomaterials. GONRs aerogel showed low density, good mechanical strength and easy separation from water. Uranium(VI) and thorium(IV) adsorption by GONRs aerogel was investigated by batch experiments, demonstrating their strongly pH-dependent, spontaneous and endothermic adsorption processes. GONRs aerogel exhibited the maximum U(VI)- and Th(IV)-uptake capacity (430.6 and 380.4 mg g−1, respectively) due to its large specific area (597.4 m2 g−1) and abundant oxygen-containing groups. This work suggests that GONRs aerogel has great potential for treatment of uranium and thorium-containing effluents.

Electrospun magnetic polyacrylonitrile-GO hybrid nanofibers for removing Cr(VI) from water

Graphene based nanocomposites powder posses an immense potential and contributes significantly in the field of water treatment applications. However, the major challenge is to separate these powder materials from the treated water, otherwise it may result in environmental pollution. In this work, Graphene oxide (GO) and Fe3O4 nanoparticles embedded polyacrylonitrile (PAN) nanofibers membrane (PAN-GO-Fe3O4) was developed by simple electrospinning technique, maintaining needle to collector distance of 15 cm, solution flow rate of 1 mL/h and applied DC voltage of 15 kV. The formation, composition, bonding, surface morphology, size, surface area, and magnetic properties of the prepared nanocomposites was analyzed by XRD, FTIR, Raman, XPS, FESEM, HRTEM, BET and VSM analytical techniques. The formation of cubic crystal structure of Fe3O4 was confirmed by XRD and HRTEM. The functionalization and surface composition of PAN-GO-Fe3O4 was confirmed by FTIR, Raman, XPS and FESEM-EDX analysis. The FESEM images revealed the formation of fine fibers of PAN-GO-Fe3O4 with diameter of 150–170 nm. The TEM image revealed that the spherical nanoparticles having diameter of 10–20 nm were decorated on the surface of PAN-GO. From the N2 adsorption-desorption experiment, it was found that PAN-GO-Fe3O4 composite shows higher surface area (90.62 mg/g) than that of GO, PAN and Fe3O4. The saturation magnetization value of the PAN-GO-Fe3O4 nanofibers membrane was found to be 28.72 emu/g. The prepared PAN-GO-Fe3O4 membrane was used for remediation of highly toxic hexavalent chromium (Cr(VI)) ions from water by batch adsorption method. The effect of Cr(VI) adsorption was investigated by varying different parameters such as amount of adsorbent, pH, time and concentration. The above experimental results revealed that Cr(VI) adsorption by PAN-GO-Fe3O4 was pH dependent and maximum adsorption capacity was found to be 124.34 mg/g. Pseudo second order kinetic model and Langmuir isotherm model were best fitted to the experimental data of Cr(VI) removal with higher correlation coefficient (R2) values. The negative value of ΔG0 and positive value of ΔH0 highlighted that the adsorption of Cr(VI) onto PAN-GO-Fe3O4 was spontaneous and endothermic process. The effect of co-existing ions and reusability test were carried out to reveal the effectiveness of the adsorbent material.

Investigation of antimony adsorption on a zirconium-porphyrin-based metal–organic framework

A zirconium-porphyrin based organic framework PCN-222 was employed for investigating the adsorption performance of Sb(III) in aqueous solution. It is proved that the adsorbent has the advantages of rapid adsorption and high capacity. Interestingly, we discover that PCN-222 shows pH-dependent adsorption performance, with higher capacity at pH = 2 and 8 than at pH = 5. According to XPS and FT-IR analyses, an adsorption model of PCN-222 with pH = 2, 5, and 8 is proposed, that is, zirconium clusters combine with antimony at different pH values with bidentate complexes, monodentate complexes, and alkaline monodentate complexes, thus producing an excellent adsorption effect. Moreover, the porphyrin ring is also beneficial for the adsorption of antimony. In addition, PCN-222 shows good regeneration and recycling performance, and it is a promising adsorbent as well as a platform for investigating the removal of Sb(III) in water treatment.

Composite synthesized from nano layered double hydroxides (or oxides) and spherical biochar: Application for removing Congo red and methylene blue dyes from water

In this study, a new composite (LDH–SB) was synthesized from layer double hydroxides (LDH) and spherical biochar (SB) through hydrothermal carbonization. LDH–SB was then calcinated at 500 ◦C to generate another composite (LDO–SB). Under such a temperature, LDH in the surface of LDH–SB was converted to layer double oxides (LDO). Their properties were thoroughly investigated. SEM images confirmed that the nano particles (LDH or LDO) were successfully loaded in the surface of SB. XRD data validated the existence of LDH or LDO in the structure of the composites. The BET surface area of LDH–SB và LDO–SB was 81.7 m2/g and 192 m2/g. The pHPZC of LDH–SB and LDO–SB was 8.49 and 10.23. Leaching test demonstrated that two composites exhibited a strong chemical stability within solution pH from 2.0 to 10. The results of pH-dependent adsorption indicated that two composites well adsorbed methylene blue (MB) dye under basic condition (pH 10) and Congo red (CR) dye under acid (pH 3.0). Adsorption kinetics, isotherms, and thermodynamics were conducted under batch experiments. The maximum adsorption capacity of the MB+ cations and CR- anions by LDH–SB (92.2 and 266 mg/g) and LDO–SB (64.4 and 795 mg/g, respectively) was calculated from the Langmuir model. LDO–SB exhibited an excellent adsorption capacity towards CR dye in water compared to LDH–SB.

Modulating hierarchically microporous biochar via molten alkali treatment for efficient adsorption removal of perfluorinated carboxylic acids from wastewater

This work presented a three-dimensional (3D) hierarchically microporous biochar (HMB) via molten alkali treatment that achieved efficient adsorption of perfluorinated carboxylic acids (PFCAs), which was a significant environment concern due to the global distribution and potential health risks. The systematic optimization of fabrication process rendered the HMB large surface area and uniform microporous structure, leading to a high adsorption capacity and adsorption rate of 1269 mg/g and 197 mg/(g·min), respectively, when perfluorooctanoic acid (PFOA) was as a representative. The adsorption mechanisms were explored via controlling the interaction between PFCAs and the HMB900-2.4. Specifically, hydrophobic effect was verified by the enhanced adsorption performance with the increase of the PFCAs homologues hydrophobicity. The observed highly pH-dependent adsorption capacity additionally suggested the dominant contribution of electrostatic interaction. For long-chain PFCAs (CnF2n+1COOH, n > 5), the HMB900-2.4 presented a high removal efficiency (> 90%) within 30 min. Even for short-chain PFCAs (CnF2n+1COOH, n = 4–5), the removal efficiency reached to over 60%. The synthesized HMB900-2.4 exhibited high stability during recycling experiments and superior performance over commercial adsorbents, suggested a promise of utilizing it to remove PFCAs from wastewater.

Efficacy of Woodchip Biochar and Brown Coal Waste as Stable Sorbents for Abatement of Bioavailable Cadmium, Lead and Zinc in Soil

Organic sorbents alter physicochemical soil properties and mitigate heavy metal (HM) bioavailability. However, some sorbents are labile and, therefore, introduce the risk of HM release into soil after mineralisation. Before field application, new stable organic sorbents such as woodchip biochar (BIO) and brown coal waste (BCW) need to be tested and compared with standard organic amendments like farmyard manure (FYM). An incubated pot experiment was conducted to investigate the efficacy of FYM, BIO and BCW (added to soil in pots at 5 and 10% w/w) to alter soil physicochemical properties and mitigate bioavailability of Cd, Pb and Zn spiked in treatments at different doses (in mg kg−1); 0 (not spiked), 1 (1 Cd, 70 Pb, 100 Zn) and 2 (3 Cd, 500 Pb, 700 Zn), and incubated for 9 weeks. At the end of the experiment, the EDTA-extractable HM fractions, pH, cation exchange capacity (CEC) and specific surface area (SSA, to check trends) were determined in all treated soils. Results showed that FYM, BCW and BIO generally improved all soil properties (except reduced pH from BCW and apparent SSA reduction from FYM) and accounted for respective maximum abatements of Cd (50.2, 69.9 and 25.5%), Pb (34.2, 64.3 and 17.4%) and Zn (14.9, 17.7 and 11.8%) bioavailability in soil. FYM and BCW were more effective at 10% w/w especially in the low contaminated soil, whereas the highest efficacy for BIO was at 5% w/w and in the high contaminated soil. The efficacies of sorption by the organic sorbents varied for different HMs and were in the orders: BCW > FYM > BIO for Cd, FYM > BCW > BIO for Pb and BIO > BCW > FYM for Zn. Soil pH and CEC were strongly correlated with HM bioavailability in all treatments and implied that immobilisation of HMs occurred via complex formation, ion exchange and pH-dependent specific adsorption. All three sorbents were beneficial as soil amendments, and in terms of HM mitigation, BCW had the highest efficacy, followed by FYM and then BIO. Considering the documented high soil stability of BCW and BIO, these results are promising for further trialling at field scale.

Mechanism of Inversion of Montmorillonite Sorption Properties by Cationic Surfactant

Organo-mineral derivatives of montmorillonite modified by salts of quaternary ammonium compounds are promising adsorbents for wastewater purification from heavy metal anions, as well as anionic dyes and pesticides. The understanding of the mechanism of anion adsorption by the example of montmorillonite modified by didecyldimethylammonium chloride cationic surfactant is expanded. The high rate of chromium anion adsorption, the appearance of adsorption capacity only during charge exchange of the surface, and the pH dependence of adsorption, including for pH-independent nitrate anions, indicate that a significant contribution to adsorption of anions is made by silanol and aluminol groups on the edge surface of the aluminosilicate layers of the mineral. The redistribution of access to various types of adsorption centers of the surface for adsorptive is the mechanism of inversion of the adsorption properties for montmorillonite. The inner negatively charged surface is screened by the double layer of the surfactant molecules that block the interlayer space. The surfactant molecules are not hydrated, which impedes delamination of the mineral in aqueous medium.

Development of Biomass-Based Anion Exchanger for the Removal of Trace Concentration of Phosphate from Water

Aluminum loaded saponified Mango Waste i.e. Al (III)–SMW adsorbent, which functions as anion exchanger, was developed by loading Al (III) onto lime treated Mango waste biomass. The characterization of adsorbent was done by an Energy Dispersive X-ray (EDX) spectroscopy and chemical analysis techniques. Elemental analysis showed an exchange of Ca (II) or K (I) from SMW with Al (III) during loading reaction via cation exchange mechanism. Phosphate adsorption is strongly pH-dependent and maximum adsorption occurs at pH around 7– 9. The maximum uptake capacity of Al (III)–SMW for phosphate was found to be 3.28 mg/g from the Langmuir isotherm model. The residual concentration of phosphate was sharply decreased by increasing the amount of Al (III)–SMW and reached less than 0.07 mg/L (from 9.7 mg/L) with the use of only 6 g/L of Al (III)–SMW whereas higher than 7 g/L successfully removed 100% of phosphate from water. The adsorbed phosphate was successfully desorbed and the adsorbent was regenerated using dilute alkali solution. Therefore, the Al (III)–SMW adsorbent investigated in this research work is expected to be a potential material for the treatment of water polluted with a trace amount of phosphate from aqueous solution.

Green synthesis of hydrophilic activated carbon supported sulfide nZVI for enhanced Pb(II) scavenging from water: Characterization, kinetics, isotherms and mechanisms

For green synthesis of nZVI with low aggregation and high antioxidation, green tea extracts were explored as reductant during the synthesis with modification by hydrophilic porous activated carbon (HPAC) and sulfidation technology. Characterization results identified the effective preparation of porous activated carbon (PAC) with microporous and mesoporous characteristics, and the successful loading of S-nZVI nanoparticles on S-nZVI@HPAC. Moreover, HPAC was identified to have a higher degree of hydrophilicity surface compared to PAC, while the S-nZVI with an atomic ratio of S/Fe (0.16) further improved the hydrophilic performance of S-nZVI@HPAC. Batch adsorption revealed that the S-nZVI@HPAC possessed a pH-dependent adsorption performance with a fast kinetic equilibrium within 120 min and an outstanding Pb(II) binding of 295.30 mg/g at pH = 5.0 and 50 °C. Thermodynamic results exhibited positive ΔH° and ΔS°, clearly indicative of the endothermic property of Pb(II) uptake onto S-nZVI@HPAC with an increase in randomness, while the negative ΔG° uncovered a favorable and spontaneous process. Furthermore, the S-nZVI@HPAC was believed to enhance the Pb(II) uptake via the synergistic effects of electrostatic attraction, chemical precipitation, complexation and reduction. The results of this work highlighted the hydrophilic porous activated carbon supported sulfide nZVI for efficient remediation of Pb(II) contaminated water.

Transport of produced water through reactive porous media

During hydraulic fracturing (or fracking) large volumes of wastewater (flow-back and produced water) are generated, which are naturally rich in heavy metals and radionuclides, such as radium. Spills may occur during operations and contaminate the groundwater. Therefore, there is an urgent need to identify a practice that can mitigate the negative impact of accidental leaks on water resources. Here, we present an experimental and modeling work on the transport of alkaline earth elements in produced water, which are congeners of radium, namely, barium (Ba2+), strontium (Sr2+), calcium (Ca2+), and magnesium (Mg2+) in addition to sodium (Na+). Column-flood tests were conducted using produced water from a shale-gas site and reactive porous media made of ubiquitous minerals such as sand, hydrous ferric oxide, activated alumina, and manganese oxide. In all cases, no retardation of the ions was observed at the salinity conditions of the produced water, but strong retardation in the pH front was measured, indicating that adsorption indeed occurred. When using manganese oxide and upon dilution of produced water, the concentration fronts of all major divalent cations were retarded. However, a fast wave of solute, traveling at the average flow velocity, emerged. This phenomenon confirmed that significant adsorption occurred under those conditions. But, pH-dependent adsorption and hydrodynamic dispersion favored fast solute transport.Overall, these results suggest that manganese oxide could be used as a reactive material in the lining of temporary storage tanks and in the well cases in order to retard the migration of the major toxic elements in produced water. However, mixing must be controlled to avoid the emergence of an instability at the concentration fronts favoring the formation of fast waves.

High and low affinity sites of ferrihydrite for metal ion adsorption: Data and modeling of the alkaline-earth ions Be, Mg, Ca, Sr, Ba, and Ra

The alkaline-earth metal ion series comprises Be, Mg, Ca, Sr, Ba, and Ra. Calcium (Ca) and magnesium (Mg) are the most abundant alkaline-earth metal ions in nature and their interaction with the mineral surfaces of metal (hydr)oxides (e.g. ferrihydrite, Fh) affects the bioavailability, mobility, and geochemical cycling of many relevant ions. The adsorption of Ca2+ and Mg2+ ions to well-characterized freshly precipitated Fh has not been extensively measured yet in systems with a large variation in pH (5–10), ionic strength (0.01–1 M), and ion adsorption (0.002–2 μmol m−2). Nor have such adsorption data been interpreted with a surface complexation model that regards the structure of the adsorbed complexes and state-of-the-art insights into the surface structure of this nanomaterial. The primary adsorption data collected in this study (M2+/Fe) were scaled in a consistent manner to the surface area of Fh derived with a recently developed probe-ion methodology, before these data were interpreted with the charge distribution (CD) model, using MO/DFT/B3LYP/6-31+G** optimized hydrated geometries to obtain independently the CD coefficients. The pH-dependent adsorption behavior of Ca and Mg is rather similar. Both cations (M2+) form predominantly bidentate inner-sphere surface complexes ((FeOH)2Δz0MΔz1), most possibly as a binuclear double corner (2C) complex according to EXAFS. This binding mechanism explains the relatively high H+/Ca2+ exchange ratio and the related pH-dependency of the Ca2+ adsorption. Modeling of the adsorption data reveals and quantifies the surface site heterogeneity of Fh, distinguishing high and low affinity sites for binding M2+ ions. The surface structure of Fh has been evaluated to rationalize this phenomenon and identify possible surface configurations. The increase in the FeOH-M2+ bond strength may be due to a redistribution of charge within specific sets of Fe1 polyhedra at the Fh surface that have in the underlying solid a set of common oxygen ions with an insufficient charge neutralization. According to our surface structural analysis of 2.2–2.8 nm particles, the FeOH site density involved (∼0.3 ± 0.1 nm−2) aggress with the surface site density of high affinity sites found by Ca2+ ion adsorption modeling (0.30 ± 0.03 nm−2). Extending our data analysis to literature data, comprising the full series of alkaline-earth ions, an increase in adsorption affinity with increase in the ionic radius of these cations was found, i.e. Be2+ < Mg2+ < Ca2+ ≈ Sr2+ < Ba2+ < Ra2+, which is opposite to the order of the Hofmeister series observed for other Fe-(hydr)oxides (e.g. hematite, goethite). The affinity trends have been evaluated with a model for ion adsorption energy developed in this study. This analysis suggests that a difference in the order of affinity (logK) can be explained by a different energy and/or entropy contribution of interfacial water in the binding of the metal ions. This points to a relatively strong binding of physisorbed water by Fh in comparison to other Fe-(hydr)oxides where the energy of ligand exchange dominates. For Fh, interfacial water is more strongly bound by high affinity sites than by low affinity sites, according to our model.

Anionic congo red dye removal from aqueous medium using Turkey tail (Trametes versicolor) fungal biomass: adsorption kinetics, isotherms, thermodynamics, reusability, and characterization

Turkey tail (Trametes versicolor), cheap fungal biomass (TTFB), was used for the adsorption of CR from aqueous medium. Batch studies conducted to study the effect of pH (2.0–10.0), agitation speed (50–400 rpm), contact time (0–180 min), adsorbate concentration (300 and 500 mg/L), and temperature (303–333 K). TTFB characterized by FTIR, BET, SEM, and pHpzc. The maximum monolayer adsorption capacities of CR on TTFB were 318.1, 368.4, 394.8, and 415.7 mg/g at 303, 313, 323, and 333 K, respectively. The adsorption of CR was pH-dependent and maximum adsorption attained at pH 2.0 at all temperatures. Adsorption kinetic data evaluated by using the PFO and PSO non-linear equations. The kinetic data perfectly illustrated by the PSO model with R 2 > 9935. Langmuir, Freundlich, D-R, and Temkin nonlinear isotherms applied for the experimental data, and it observed that the experimental data well fitted and found to be in good agreement with the Langmuir model (R 2 > 0.9961) as compared with another three models. The values of ΔG° (–3.4159 to −6.1149 kJ/mol), ΔH° (23.2 kJ/mol), and ΔS° (0.088 kJ/mol K) revealed that the adsorption process was spontaneous, feasible and endothermic (ΔG° < 0, ΔS° > 0, and ΔH° > 0). The regeneration experiments indicated that the TTFB could successfully retain CR, even after five consecutive adsorption-desorption cycles. The binding of CR onto the TTFB surface was through electrostatic interactions. Therefore, TTFB considered as highly recyclable and efficient adsorbent material for CR as it can easily separate from the aqueous phase.

Simultaneously enhanced removal and stepwise recovery of atrazine and Pb(II) from water using β–cyclodextrin functionalized cellulose: Characterization, adsorptive performance and mechanism exploration

Heavy metals and pesticides often coexist in contaminated water, while their potential competition behaviors make the adsorptive removal more challenging. Thus, decorating an adsorbent with independent functional sites could be a promising alternative to radically prevent the competitive process for improving the adsorption performance. Herein, β-cyclodextrin functionalized rice husk-based cellulose (β-CD@RH-C) was designed and applied for synchronous removal of atrazine and Pb(II). The characterization results supported the successful grafting of β-cyclodextrin onto the cellulose. The β-CD@RH-C presented a pH-dependent adsorption performance for Pb(II) with a theoretical monolayer adsorption capacity of 283.00 mg/g, while was mostly unrelated to pH for atrazine adsorption with a heterogeneous uptake of 162.21 mg/g in the mono-component system. Most importantly, the β-CD@RH-C could efficiently achieve simultaneous removal of atrazine and Pb(II) via avoiding their competitive behaviors, which was due to the different adsorption mechanisms for atrazine (i.e. host-guest interaction) and Pb(II) (i.e. complexation and electrostatic interaction). Moreover, the adsorbed atrazine and Pb(II) could be sequentially desorbed with slight decrease in the adsorption performance of β-CD@RH-C even after four cycles in the atrazine-Pb(II) multi-component system. All these results suggested β-CD@RH-C to be a tailored adsorbent with high-performance elimination of co-existing heavy metals and organic pollutants in water.

Green synthesis of Fe2O3-Ag nanocomposite using Psidium guajava leaf extract: An eco-friendly and recyclable adsorbent for remediation of Cr(VI) from aqueous media

An environmental friendly and cost effective method was used for the preparation of silver‑iron oxide (α-Fe2O3-Ag) nanocomposite using guava (Psidium guajava) leaf extract, which can be used as an adsorbent for decontamination of chromium (VI) ions from aqueous media. XRD analysis revealed that both Iron oxide and silver nanoparticles are crystalline in nature with face-centered cubic and rhombohedral geometry respectively. The FESEM micrographs of Fe2O3-Ag nanocomposite displayed irregular shaped particles with an average size of 50–90 nm. BET surface area analysis suggests that the prepared Fe2O3-Ag nanocomposites are mesoporous in nature with surface area of 122.72 m2/g. The adsorption of Cr(VI) was pH dependent and maximum adsorption occurred at pH = 4 with maximum adsorption capacity of 71.34 mg/g. Thermodynamic parameters reveals that the Cr(VI) adsorption on Fe2O3-Ag surface is endothermic and spontaneous in nature. The adsorbed Cr(VI) on Fe2O3-Ag surface was recovered and can be reused up to five cycles.

Cationic polyelectrolyte grafted mesoporous magnetic silica composite particles for targeted drug delivery and thrombolysis

Magnetic iron oxide (Fe3O4) microparticles prepared by solvothermal route are modified with SiO2 layer and then functionalized with vinyl groups. Finally, polyelectrolyte layer composed of isobornyl methacrylate (iBMA) and (3-acrylamidopropyl)trimethylammonium chloride (APTMACl) is grafted onto the surface of magnetic SiO2 particles via free radical polymerization to produce composite particles abbreviated as Fe3O4/SiO2/P(iBMA-APTMACl). The size distribution and structural composition of Fe3O4/SiO2/P(iBMA-APTMACl) composite particles are measured by electron microscopy and different spectroscopy techniques. Fe3O4/SiO2/P(iBMA-APTMACl) composite particles possessed moderate paramagnetic property. The mesoporous surface structure of composite particles is confirmed from average pore diameter (3.8 nm), measured by Barrett–Joyner–Halenda (BJH) method. The composite particles exhibited pH dependent phase transition near 5.8. The pH dependent adsorption and release study of anionic drug (aspirin) through off- and on-capping of polyelectrolyte valve/gate confirmed the ion exchange property of Fe3O4/SiO2/P(iBMA-APTMACl) composite particles. Compared to Fe3O4/SiO2 particles, the loading capacity of biomolecules in polyelectrolyte grafted composite particles (∼ 30 mg g−1) is relatively larger at the respective isoelectric point. In presence of 11.2 kU mg−1 conjugated streptokinase (SK), Fe3O4/SiO2/P(iBMA-APTMACl) composite particles exhibited significant amount of thrombolytic activity (56%). A brief study of hemolysis suggested that composite particles are hemocompatible up to 0.18 mg mL−1. The higher inhibition percentage of protein denaturation also indicated the anti-inflammatory property of bare composite particles. The prepared Fe3O4/SiO2/P(iBMA-APTMACl) composite particles can therefore be applied in targeted thrombolysis, drug/gene carrier, anti-inflammatory agent and hyperthermia.

PH-Dependent adsorption of aromatic compounds on graphene oxide: An experimental, molecular dynamics simulation and density functional theory investigation

This work provides a comprehensive understanding for the pH-dependent adsorption of aromatic compounds (ACs) on graphene oxide (GO). Isothermal and kinetics experiments indicated both adsorption capacity and adsorption rate were suppressed at higher pH, and the mechanisms were revealed by molecular dynamics simulations and density functional theory calculations. More specifically, π-π, hydrogen bond, vdWs, and water-mediated steric hindrance interactions were examined to reveal how pH affected the adsorption capacity, and microscopic dynamic adsorption process was captured to reveal how pH affected the adsorption rate. Results showed the reduced adsorption capacity at higher pH was mediated by increased electrostatic repulsion, weakened π-π interaction, and increased water-mediated steric hindrance. The pH-dependent behaviour of GO was responsible for the effect of pH on adsorption rate. Self-aggregation of GO at lower pH helped to capture ACs and created more favourable adsorption sites. Upon the adsorption of ACs on GO, GO/water/AC/water/GO sandwich-like structure formed, which was also mediated by solution pH. Overall, pH affects the adsorption of ACs on GO by regulating driving forces, adsorption process, and the configuration property of GOAC complex.

High performance of phytic acid-functionalized spherical poly-phenylglycine particles for removal of heavy metal ions

In the present work, a novel material consisting of phytic acid-functionalized poly-phenylglycine (PA-PPG) was successfully synthesized through radical polymerization and used for the removal of heavy metals ions from water. Microscopic images revealed the formation of homogenous particles in aggregated form. The chemical composition of the PA-PPG was examined using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. The influence of various experimental parameters such as solution pH, alkaline metals, and initial concentration of Cu, Pb, Cd ions on the removal efficiency of PA-PPG was assessed by using absorption atomic spectroscopy (AAS). The PA-PPG sample exhibited high maximum adsorption capacity of 90.5, 732.4, and 216 mg/g for Cu, Pb, and Cd ions, respectively. The PA-PPG demonstrated a pH-dependent adsorption with a maximum adsorption capacity achieved at pH 5.2. The Langmuir and Temkin models described well the adsorption isotherm data and a probable adsorption mechanism based on complexation and electrostatic attraction was proposed. Moreover, the developed PA-PPG can be reused for four cycles without any apparent loss of its adsorption capacity. The obtained results prove the efficiency of phytic acid, validate and promote the idea of using an active molecule to enhance the capacity of poly-phenylglycine for environmental remediation.

Ultrafast and highly capture of U(VI) by hierarchical mesoporous carbon

Abstract In this study, the hierarchical mesoporous carbon (HMC) was synthesized by the hydrothermal method. The batch adsorption experiments showed that HMC exhibited the ultrafast equilibrium fate (80 % U(VI) capture efficiency within 5 min), high UO2 2+ capture capacity (210 mg/g, pH = 4.5) and well recyclability. The investigations of XPS techniques indicated the oxygen-containing functional groups were responsible for high efficient UO2 2+ adsorption. The pH-dependent adsorption was simulated by three surface complexation modellings, revealing that UO2 2+ adsorption on HMC was excellently fitted by triple layer model using two inner-sphere complexes (i. e. SOUO2 + and SOUO2(CO3)3 5− species) compared to constant capacitance model and diffuse layer model. These findings are crucial for expanding actual applications of HMC towards the removal of radionuclides under environmental cleanup.

Determining roles of in-situ measured surface potentials of phase controlled synthesized MnO2 nanostructures for superficial adsorption

Adsorption is one of options for environmental remediation. Current works focused on designing nanostructures, and ex-situ measured specific area and zeta potential were main descriptors for the adsorption performance, leaving the materials’ intrinsic features irrelevant to adsorption. Herein, to investigate the adsorption performance and adsorbent inherent characteristics, an in-situ measurement of zeta potential was presented by taking MnO2 adsorbing methylene blue (MB) as an example. The performance was randomly related between ex-situ measured specific areas and zeta potentials of MnO2, but the in-situ measured MnO2 zeta potentials in 10 and 100 mg·L−1 MB solutions both showed nonlinear hyperbolic relationship with the performance, confirming the significant role of in-situ zeta potentials. Furthermore, adsorption enhancement in low pH conditions was observed, for Mn(IV) oxidability promoted by acidic solutions, where MB redox was oxidized to the positively charged oxidized form, facilitating adsorption onto negatively charged MnO2. The adsorption performance of MnO2 with considerably low specific area was comparable to reported nanostructured metal oxide adsorbents, showing the importance of surface zeta potentials and oxidability. An insight into the adsorption affecting factors within the inherent features of adsorbents was presented through in-situ measured zeta potentials and pH dependent adsorption.