Competition For Adsorption Sites Research Articles

Simultaneous removal of U(VI) and tetracycline from aqueous solution by biochar-supported nano-hydroxyapatite: New insights into the role of biochar and interactions between pollutants

U(VI) and tetracycline (TC) in hospital wastewater pose serious threats to human health and the environment. In this study, agricultural corn straw residue was utilized as a precursor for biochar, and biochar-supported nano-hydroxyapatite (nHAP) adsorbents (CSPCs) were synthesized at various ratios. These CSPCs were employed for the removal of U(VI) and TC in both one-component and two-component systems. In the one-component system, the adsorption capacity of the material was related to the ratio of nHAP to biomass, and the maximum adsorption capacities of CSPC-1 (nHAP/biomass = 1/1) for U(VI) and TC were 724.63 mg g−1 and 15.06 mg g−1, respectively. The XPS and XRD results confirmed that biochar promoted the dissolution and precipitation of U(VI) by nHAP, which stabilized the adsorption of U(VI) by CSPC-1. In the two-component system, the complexation strength of U(VI) and TC had a significant effect on the adsorption of both. At pH < 3.0, U(VI) inhibited the adsorption of TC, whereas TC enhanced the adsorption of U(VI). However, at pH > 4.0, the adsorption of U(VI) and TC were mutually reinforcing. At pH = 5.0, TC inhibited the adsorption of U(VI) only when the concentration of TC was significantly greater than that of U(VI). Combined with the systematic analysis of the FTIR, XPS and Raman spectroscopic results, these results suggest that these phenomena can be attributed to the complexation-bridging interactions between U(VI) and TC and their competition for adsorption sites.

Hydroxyapatite incorporated metakaolin/sludge based geopolymer adsorbent for copper ions and ciprofloxacin removal: Synthesis, characterization and mechanisms

The efficacy of copper Cu(II) adsorption is significantly affected by the presence of antibiotics, such as ciprofloxacin (CIP). Therefore, researchers are highly interested in conducting extensive investigations on the simultaneous adsorption of Cu(II) and CIP. However, most of the adsorbents exhibited low adsorption capacity of CIP with increasing Cu(II) concentration due to the competition for adsorption sites. Hence, the integration of various adsorbents into a single composite could be an effective way to increase the adsorption sites. Thus, this study aims to incorporate hydroxyapatite (Hap) into metakaolin/sludge based geopolymer adsorbent for simultaneous adsorption of Cu(II) and CIP. The effect of different filler loading of Hap (1–3 %) on the metakaolin/sludge geopolymerization and also on the removal efficiency of Cu(II) and CIP were studied in a single and binary system. Moreover, the effects of varied concentrations of Cu(II) (0–100 mg/L) on the removal efficiency of CIP were investigated. Characterization techniques such as x-ray diffraction (XRD), fourier-transform infrared spectrometry (FTIR), scanning electron microscopy (SEM), brunauer-emmett-teller (BET) and neutron tomography imaging were employed to characterize the physicochemical properties of the synthesized geopolymer. It was found that the Hap content has a significant impact on the removal efficiency of CIP and Cu(II). The addition of 2 % Hap providing more nucleation site for the increasing geopolymerization (C-A-S-H) and silicoalumino phosphate gel (SAP) leading to the formation of highly cross-linked geopolymer network and abundant active sites which would favour the adsorption. Moreover, the removal efficiency of CIP by 2 % Hap-geopolymer increased (25.6 % to 61.51 %) with increasing Cu(II) concentration by the complexation and bridging effect between Cu(II) and CIP resulting in the formation of GMK25S1-2Hap-Cu(II)-CIP complexes. Therefore, the hybrid method of geopolymer and Hap is an exceptionally efficient approach for the treatment of wastewater that comprises Cu(II) and CIP.

Simultaneous adsorption of Ciprofloxacin and Ni(II) from wastewater using poly(vinyl alcohol)/poly(sodium-p-styrene-sulfonate) semi-interpenetrating polymer network@Ni foam: Insights into the synergistic and antagonistic mechanisms

The coexistence of antibiotics and heavy metals in wastewater notably influences their adsorption removal behavior. However, the synergistic and antagonistic characteristics and mechanisms of their co-adsorption remain unclear. A novel adsorbent, PVA/PSSNa semi-IPN@Ni foam, was synthesized and applied to study its features and mechanisms in the single and binary systems of ciprofloxacin (CIP) and Ni(II). Exceptional removal efficiencies of 95.17 % for CIP and 99.20 % for Ni(II) were achieved. The interactive effects between CIP and Ni(II) were comprehensively explored through adsorption capacity ratio (Rq) and response surface methodology. Mechanistic insights were obtained through NaCl charge shielding experiments, substructure analog molecule probes experiments, theory calculations, as well as FTIR and XPS characterizations. The outcomes suggest that in the single system of CIP, the adsorption mechanisms include electrostatic attraction, hydrogen bonding, and π-π interactions. In the single system of Ni(II), mechanisms include electrostatic attraction and coordination. In the binary system of CIP + Ni(II), low Ni(II) concentrations facilitate CIP adsorption through coordination and bridging, whereas high Ni(II) concentrations let to competition for adsorption sites. Interestingly, the presence of CIP had minimal impact on Ni(II), exhibiting only a slight synergistic effect. These findings highlight the PVA/PSSNa semi-IPN@Ni foam as a hopeful candidate for removing CIP and Ni(II) from wastewater, and contribute to a deeper comprehension of synergistic and antagonistic mechanisms in the binary system involving CIP and Ni(II).

Effects of chloride on corrosion scale compositions and heavy metal release in drinking water distribution systems

Variations in water chemistry may lead to the release of harmful heavy metals in drinking water distribution systems (DWDSs). In this study, the effects of chloride on the release of heavy metals such as Fe, Mn, As, Cr, Mo, V, Sr, and Co were examined using steel and cast iron pipe loops. After chloride was added, the relative contents of goethite (α-FeOOH), lepidocrocite (γ-FeOOH), and siderite (FeCO3) in pipe scales increased, but the contents of magnetite (Fe3O4) decreased. The most prevalent compounds were α-FeOOH and γ-FeOOH. When the chloride levels were increased, the effluent concentrations of Fe, Mn, As, Cr, Mo, V, Sr, and Co significantly increased. These heavy metals were released presumably because of the destabilization and dissolution of corrosion scales induced by chloride and adsorption site competition. Strong positive correlations were also observed between Fe&Mn, Fe/Mn&As, Fe/Mn&Cr, Fe/Mn&Mo, Fe/Mn&V, Fe/Mn&Sr, and Fe/Mn&Co, indicating the co-release of Fe, Mn, and other metals. This study may be helpful for the potential strategies on avoidance of heavy metal release and improvement of water supply security.

Pharmaceutical adsorption on NaOH-treated rice husk-based activated carbons: Kinetics, thermodynamics, and mechanisms

This study aims to explore the adsorption behavior of four pharmaceuticals: ciprofloxacin (CIP), sulfamethoxazole (SUL), diclofenac (DIC), and acetaminophen (ACE) on activated carbons produced from rice husk using different NaOH-based protocols at 800 °C. The main objective is to assess and compare the efficiency of activated carbons synthesized by solid-solid and wet treatment methods on pharmaceutical adsorption. All three activated carbons displayed strong affinity towards pharmaceutical adsorption, but the material produced with wet protocol after the carbonization process demonstrated the highest adsorption capacity and the lowest equilibrium time (15 min) due to its superior textural properties and higher surface area (1671 ± 31 m2 g−1). Further investigation of pharmaceutical adsorption in synthetic urine was carried out using the mentioned material. The results revealed that in both mono and multicomponent systems, CIP, SUL, and DIC did not exhibit any significant competition with each other or with the urine matrix. However, ACE showed competition for adsorption sites. For both CIP and ACE, the diffusion boundary layer and the adsorption process were identified as the velocity-limiting steps for adsorption in urine. To better understand the adsorption mechanism, both experimental and computational tools were employed. The results revealed that ACE exhibited typical Langmuir-like adsorption behavior with an exothermic nature on the mentioned material with an adsorption capacity of 209.6 ± 5.6 mg g−1. Regarding CIP, its adsorption displayed a non-typical endothermic nature, which was attributed to steric hindrance due to its zwitterionic structure and the porosity in the adsorbent. Analyzing the combination of Redlich-Peterson and Langmuir models with computational analysis supported this finding. However, the material exhibited an impressive adsorption capability of 584.4 ± 21.5 mg g−1. The parameter φ (cncreased cost associated with enhancing the adsorption process) revealed an augmentation in adsorption capacities of 45.1 and 125.6 mg USD−1 for ACE and CIP, respectively, compared to the raw rice husk. This research underscores the prospect of employing agricultural and industrial byproducts to create activated carbons capable of efficiently extracting pharmaceuticals from intricate mixtures, such as urine.

Role of CO2 on trace arsenic and selenium separation from coal-fired flue gas by CaO

Coal-fired power plants have been recognized as a major source of arsenic and selenium emissions. Considering that the common temperature window exists, in which both As2O3, SeO2 and CO2 can be effectively captured by CaO-based adsorbents, new principles of CO2 presence affecting arsenic and selenium removal process were investigated by density functional theory (DFT) calculations. The results confirm the suppression role of CO2 on As2O3/SeO2 adsorption by CaO (100) surface. On the basis of single-molecule adsorption on CaO, the adsorption energies of As2O3 and SeO2 are −2.21 eV and −2.05 eV, which are stronger than that of CO2. Three molecules can be chemically adsorbed on CaO with the surface O atom as active sites, leading to the competition for adsorption sites on the CaO surface. Despite the higher preferential adsorption of As2O3 and SeO2 on CaO (100) than CO2, the presence of CO2 weakens the electron transfers from the surface O atoms to As and Se atoms in the co-adsorption configurations. Under the atmosphere of high-concentration CO2, the adsorption of CO2 on CaO surface primarily changes the original electronic field of CaO (100) surface, and abolishes the function of O sites for As2O3/SeO2 adsorption at the final stage of complete carbonation. As2O3 and SeO2 adsorb on the fully carbonated CaO surface by physisorption. The bond population and density of states verify that the presence of CO2 weakens the covalent bonds between the surface O atoms and As/Se atoms, and brings about the intermolecular repulsion in the following As2O3/SeO2 adsorption. In addition, the negative effect of CO2 on arsenic capture by CaO is more pronounced than that on selenium capture. Finally, four mechanisms including isolation mode, competition mode, low-degree carbonation mode and high-degree carbonation mode are determined to gain further insight into the structure-reaction correlation during arsenic and selenium removal from the microscopic aspect.

Simultaneous adsorption of hydrophilic and lipophilic dyes on iron-doped hydroxyapatite/carbon dots nanocomposites

Nanocomposites of iron-doped hydroxyapatite and carbon dots were synthesized through green synthesis processes, using Yerba Mate (Ilex paraguariensis) as a precursor. A thorough characterization of the particles was carried out by HRTEM, XRD, FTIR, DLS, XPD, and static contact angle. The characterization indicated that the crystallinity, surface charge, and wettability depend on the synthesis parameters.Carbon dots-doped materials, YMnAp@CD and YMFenAp@CD, showed amphiphilic properties with the capacity to adsorb Crystal violet (CV) and Oil Blue A (OBA) from aqueous or toluene-based solutions. The mentioned materials showed the highest number of adsorption sites, with values of 2.95 ± 0.05 and 3.18 ± 0.04 mmol CV/gads and 1.65 ± 0.02 0.97 ± 0.06 mmol OBA/gads on monocomponent systems, and through a multi-component analysis, the competition for adsorption sites was elucidated.

Impact of biochar colloids on thallium(I) transport in water-saturated porous media: Effects of pH and ionic strength

Understanding the migration behavior of thallium (TI) in subsurface environments is essential for Tl pollution prevention. With the wide production and utilization of biochar, the notable ability of biochar colloids to carry environmental contaminants may make these colloids important for Tl(I) mobility. This study systematically investigated the impact of wood-derived biochar (WB) and corn straw-derived biochar (CB) colloids on Tl(I) transport in water-saturated porous media under different pH (5, 7 and 10) and ionic strengths (ISs) (1, 5 and 50 mM NaNO3). WB colloids improved Tl(I) transport under all IS conditions at pH 7 due to the adsorption capacity of biochar and competition for adsorption sites on the sand surface. However, at IS 50 mM, CB colloids slightly impeded Tl(I) mobility due to the straining. In addition, both WB and CB colloids accelerated Tl(I) mobility under all pH conditions at IS 5 mM. At pH 10, the promotion effect was more obvious due to the deprotonation of O-containing functional groups and higher fluidity of biochar colloids. Furthermore, the two-site nonequilibrium model and two-site kinetic attachment/detachment model suitably described the breakthrough curves (BTCs) of Tl(I) and biochar colloids, respectively. The colloid-facilitated solute transport model could also describe Tl(I) transport influenced by biochar colloids reasonably well. This study provides insight into the migration and fate of Tl(I) in the presence of biochar colloids.

Effect of dissolved humic acids and coated humic acids on tetracycline adsorption by K2CO3-activated magnetic biochar

Humic acids (HAs) widely exist in water environment, and has an important impact on the adsorption of pollutants. Herein, HAs (both dissolved and coated) was employed to assess the effect on the removal of the organic contaminant tetracycline (TC) by K2CO3 modified magnetic biochar (KMBC). Results showed that low concentration of dissolved HAs promoted TC removal, likely due to a bridging effect, while higher concentration of dissolved HAs inhibited TC adsorption because of the competition of adsorption sites on KMBC. By characterization analysis, coated HAs changed the surface and pore characteristics of KMBC, which suppressed the TC removal. In a sequential adsorption experiment involving dissolved HAs and TC, the addition of HAs at the end of the experiment led to the formation of HAs-TC ligands with free TC, which improved the adsorption capacity of TC. TC adsorption by KMBC in the presence of dissolved HAs and coated HAs showed a downward trend with increasing pH from 5.0 to 10.0. The TC adsorption process was favorable and endothermic, and could be better simulated by pseudo-second-order kinetics and Freundlich isotherm model. Hydrogen bonds and π–π interactions were hypothesized to be the underlying influencing mechanisms.

Effective mitigation of ammonia in sewage-sludge-derived fermentation liquid using flow-electrode capacitive deionization

Due to the high toxicity of ammonia to organisms and its contribution to eutrophication in surface water, the risk of emission of ammonia and other nitrogenous ions to the environment and ecosystems has aroused wide concerns. Therefore, the discharge criterion on nitrogen in effluent from conventional wastewater treatment plants (WWTP) is very stringent. Furthermore, during the conventional denitrification processes, the relatively costly external carbon source is usually required. Nowadays production of volatile fatty acids (VFAs) from sewage sludge by alkaline anaerobic fermentation has regarded as an attractive carbon source. However, usually ammonia is quite abundant in the fermentation liquid and thus effective mitigation of ammonia in the fermentation liquid is also a significant step for its further utilization. In the present study, the flow electrode capacitive deionization (FCDI) was applied to remove ammonia in the fermentation liquid of sewage sludge. Firstly, response surface method (RSM) was employed to optimize parameters and then the performance of the FCDI in ammonia removal were examined. Results showed that optimal flow rates, carbon content and ammonia concentration were 8.0 mL min−1, 4.0 wt% and 110 mg N·L−1 and the ammonia removal efficiency (ARE) reached 42.7%, while treating the alkaline fermentation liquid. Seemingly the presence of Na+ and polypeptides in the liquid with their average RE of 53.3% and 11.1% substantially compromised ammonia removal probably due to the competition of adsorption sites. This present study serves as a proven concept for the feasibility of the application of the FCDI system in ammonia separation from the VFAs, which could realize economic and ecological benefits.

Contribution of components in natural soil to Cd and Pb competitive adsorption: Semi-quantitative to quantitative analysis

Cadmium (Cd) and lead (Pb) are two of the most common elements found in contaminated sites. The behavior of specific metals in the soil may be affected by other metals because of the competition for adsorption sites. In this study, adsorption experiments after chemical extraction, multi-surface models, and advanced spectroscopy technology were jointly used to explain the adsorption mechanism of Cd and Pb and to determine the contribution of each component in the competitive system. The results show that pH is the key factor in determining the contribution of soil components to metal adsorption. Soil organic matter (SOM) is the dominant adsorbent for both Cd and Pb. Clay minerals play an adsorption role at low pH, whereas Fe/Al oxides adsorb metals primarily in the high pH range. Further, the competitive effect of Pb on Cd occurred primarily on SOM rather than on clay minerals. When the Pb concentration increased from 0 to 500 mg/L, the adsorption of Cd on SOM decreased by 132.0 mg/kg, whereas it decreased only by 1.9 mg/kg on clay minerals. Therefore, the competitive effect of Pb on Cd cannot be ignored in soils with high organic matter content.

Competition for adsorption sites between atomic Be and Si on W(100)

It has been shown that Be deposition onto W(100) at 1100-1200 K results in displacement of earlier deposited Si atoms from the surface into the bulk, and the displacement is performed in “atom-to atom” mode, so that the total concentration of both adsorbates stays constant. Dissolution of Be atoms into the substrate at 1400 K leads to Si coming out from the bulk to surface. We attribute this to the fact that Be is adsorbed similarly to p-block atoms that form surface compounds on the (100) face of bcc metals.

The mechanisms involved into the inhibitory effects of ionic liquids chemistry on adsorption performance of ciprofloxacin onto inorganic minerals

The ionic liquids (ILs) can influence the adsorption of antibiotics on minerals but there was ambiguity about mechanisms. Herein, we demonstrated the adsorption characteristics of ciprofloxacin (CIP) onto ferrihydrite and montmorillonite by various soluble ILs. Five imidazolium-based ILs with different alkyl chain lengths ([C2mim]Cl, [C4mim]Cl, [C6mim]Cl) and counteranions ([C4mim][TOS] and [C4mim][PF6]) were employed. The results validated that ILs could suppress CIP adsorption on both minerals due to the adsorption site competition between cations and CIP molecules, steric hindrance induced by long alkyl chains of ILs, and electrostatic interaction. Interestingly, the adsorption-inhibition effects of ILs were almost unchanged with the lengthening alkyl chain for ferrihydrite, which were ascribed to the comparable adsorption capacities of the three ILs on ferrihydrite. Whereas, the effects of ILs on CIP adsorption onto montmorillonite followed the order of [C6mim]Cl > [C4mim]Cl > [C2mim]Cl owing to the adsorption site competition and steric hindrance effects on the ILs increased with the lengthening alkyl chain. Furthermore, the inhibitory effects of ILs on CIP adsorption onto both studied minerals were also dependent on the counteranions (kept the same cation ([C4mim]+)) and in the following order of [C4mim][PF6] > [C4mim][TOS] > [C4mim]Cl, which was mainly ascribed to the differences of anions in the ion sizes and the binding affinities to minerals. Additionally, the extent of the inhibitory impact of [C4mim][TOS] on CIP adsorption onto ferrihydrite declined with increasing solution pH from 5.0 to 9.0, which was attributed to the amounts of adsorbed [TOS]– declined with increasing pH. Contrarily, for montmorillonite, the extent increased with increasing pH, owing to increase in adsorption site competition and steric effect at higher pH conditions. Our findings emphasize the significance of emerging contaminants in understanding the antibiotic environmental behavior in eco-environmental systems.

Quinone-mediated Sb removal from sulfate-rich wastewater by anaerobic granular sludge: Performance and mechanisms

Antimony (Sb) is a typical pollutant in sulfate-rich industrial wastewater. This study investigated the Sb removal efficiency in sulfate-rich water by anaerobic granular sludge (AnGS) and the stimulation of amended anthraquinone-2-sulfonate (AQS). Results showed that 89.0% of 5 mg/L Sb(V) was reduced by AnGS within 24 h, along with the observed first accumulation (up to 552.2 μg/L) and then precipitation of Sb(Ш); coexistence of 2 g/L sulfate inhibited the removal of Sb(V) by 71.4% within 24 h, along with gradual accumulation of Sb(Ш) by 3257.4 μg/L, indicating the potential competition of adsorption sites and electron donors between Sb(V) and sulfate. Amendment of 31 mg/L AQS successfully removed the inhibition from sulfate, contributing to 99.5% Sb(V) removal and minimum Sb(Ш) accumulation in Sb(V) + sulfate+AQS group. Further test results suggested that Sb(V) removal by AnGS was mainly through dissimilatory reduction instead of bio-sorption, while Sb(Ш) removal mainly relied on instant bio-sorption by AnGS followed by precipitation in the form of Sb2O3 and Sb2S3. Extracellular Polymeric Substances (EPS) characterization showed that AQS promoted the accumulation of Sb(V) and Sb(Ш) in EPS. High-throughput sequencing analysis showed the enrichment of sulfate-reducing bacteria (SRB) in Sb(V) + sulfate group and suppressed SRB growth in Sb(V) + sulfate+AQS group.

Arsenic(III) and Arsenic(V) Removal from Water Sources by Molecularly Imprinted Polymers (MIPs): A Mini Review of Recent Developments

The present review article summarizes the recent findings reported in the literature with regard to the use of molecularly imprinted polymers for the removal of arsenic from water and wastewater. MIPs are polymers in which a template is employed in order to enable the formation of recognition sites during the covalent assembly of the bulk phase, via a polymerization or polycondensation process. The efficiency of both arsenic species and the mechanism of removal are highlighted. The results have shown that under certain conditions, MIPs demonstrated arsenic sorption capacities of up to 130 mg/g for As(V) and 151 mg/g for As(III), while the regeneration ability was found to reach up to more than 20 cycles. The overall results showed that further development of MIPs could result in the formation of promising adsorbents for arsenic removal from waters. The use of MIPs for the removal not only of arsenic but also other inorganic contaminants is considered a very important topic, with great potential in terms of future applications in water treatment. The main advantage of these materials is that they are very selective toward the contaminant of interest. This enhanced selectivity is attributed to the incorporation of specific templates, which can then adsorb the contaminant of interest almost exclusively. Therefore, the main problem in adsorption processes is the competition for adsorption sites by other water components, for example, phosphates, nitrates, carbonates, and sulfates, which can be circumvented by the use of MI-type adsorbents.

Butynediol’s Role beyond Brightening Additive during Electrodeposition of Cobalt

Butynediol (2-Butyne-1,4-diol), a well-known type-II brightening additive, changes the interfacial pH resulting in the formation of porous cobalt hydroxide film of ca. 1 μm thickness over the copper substrate in a short duration of electrodeposition (2 min) and at a very low current density (−5 mA cm−2) from sulfate bath. In the absence of butynediol, a metallic cobalt layer was observed under identical deposition conditions. The choice of anions (sulfates, chlorides and nitrates) in the electrodeposition bath determines the kind of electrodeposited films obtained, viz., cobalt, cobalt/cobalt hydroxide, and compact cobalt hydroxide. The adsorption of butynediol enhances hydrogen evolution due to water reduction that facilitates the formation of porous microstructures of cobalt hydroxide. Competition for adsorption sites between butynediol and chloride and dissolution of cobalt hydroxide by diffusing protons result in a mixed metallic cobalt particle and porous cobalt hydroxide microstructure. The variations in the phases and microstructures of electrodeposits were evidenced through the difference in the magnetic and electrocatalytic properties.

Adsorption behavior and mechanism of tetracycline onto hematite: Effects of low-molecular-weight organic acids

Tetracycline (TC) is known to be one of the most widely used antibiotics and is released into the natural environment, where amounts of iron oxides exist. Low-molecular-weight organic acids (LMWOAs), widespread water-soluble organic substances in the eco-environment systems, may affect the interactions between iron oxides and TC molecules. Nevertheless, our knowledge about the impacts of LMWOAs on the adsorption process of TC onto iron oxides still remains incomplete. In this study, we investigated the adsorption characteristics of TC onto hematite (as a model iron oxide) with various LMWOAs (i.e., acetic acid, glycolic acid, oxalic acid, malic acid, and citric acid). The results clearly showed that LMWOAs suppressed TC adsorption onto hematite particles at pH 7.0 (e.g., the maximum adsorption amounts (qmax) decreased from 9.05 mg/g (without LMWOAs) to 5.90 mg/g (with 0.5 mM citric acid)), which was mainly ascribed to the competitive adsorption between TC and LMWOAs on the hematite surface, the increased electrostatic repulsion between negatively charged iron oxide particles and TC– species, and the steric hindrance. Additionally, divalent cations (Ca2+ and Cu2+) enhanced the adsorption-inhibition effects by forming cation-bridging with deprotonated LMWOAs. Interestingly, different mechanisms were involved in the adsorption process with increasing pH from 3.0 to 10.0. At pH < 5.0, electrostatic repulsion, adsorption site competition, and steric effect co-controlled the inhibitory effects. Differently, at pH > 5.0, electrostatic repulsion solely dominated the adsorption-inhibition effects. The findings of this study reveal that ubiquitous LMWOAs are critical factors controlling the fate of antibiotics in the natural environment.

Simultaneous removal of pollutants from sub-nanometric to nanometric scales by hierarchical dendrimers modified aerogels

The disposal of dyestuff wastewater containing metal ions and dyes is a tough challenge, due to the competition of adsorption sites. Here, aramid nanofiber (ANF) based aerogels are fabricated, which exhibit excellent adsorption performance for sub-nanometric and nanometric adsorbates, such as Cu2+ and Congo red (CR) in this work. Synthesized hierarchical polyhedral oligomeric silsesquioxanes (POSS) cored polyamide amine (PPAMAM) is used to modify ANF aerogels and molecular dynamics simulation results indicate that the POSS core endows synthesized PPAMAM with cavities and mobile terminal groups on ANF surface, compared to normal PAMAM. When prepared aerogels are applied to treat wastewater with co-adsorbate, small metal ions could enter the cavities and coordinate with internal tertiary amines. In contrast, CR molecules are too large to enter cavities and prefer interacting with external primary amines. In addition, blending PPAMAM also increases the specific surface area, which highly enhances the adsorption performance. As a result, simultaneous and effective removal of Cu2+ and CR is achieved, and in binary system, the adsorption capacities are 248.49 and 1502.95 mg/g, respectively. After five cycles, fabricated adsorbents still maintain excellent adsorption performance. Therefore, this work provides a new way to the preparation of effective adsorbents for simultaneous removal of different sized pollutants.

Adsorption of anionic surfactant in graphite oxide: A study for treatment of laundry wastewater

Laundry wastewater, when discharged directly into water bodies, is an environmental problem due to the high load of pollutants it contains particularly surfactant compounds that are difficult to treat by conventional processes. In this work, we evaluated the behavior of graphite oxide (GO) synthesized by the Hummer method for adsorption retention of such surfactant compounds. The adsorbent material used was graphite oxide prepared with recycled graphite from lithium batteries. The applicability of graphite oxide in the adsorption of anionic surfactant was evaluated by adsorption kinetics and physicochemical characterization, before and after adsorption, using sensitive techniques such as XRD, SEM, AFM, Raman spectroscopy and MIR-FTIR. The results showed that the adsorption kinetics well represented by the pseudo-second-order model indicating chemical interactions between surfactants and graphite oxide, with qe,calc (238.09 mg g−1) close to qe,exp (227.96 mg g−1), suggesting that pre-filtering decreases competition for adsorption sites. This result is promising for the treatment of anionic surfactants, which are the main pollutants in laundry wastewater.

Cotransport of micro- and nano-plastics with chlortetracycline hydrochloride in saturated porous media: Effects of physicochemical heterogeneities and ionic strength

Global production and use of plastics have resulted in the wide dissemination of micro- and nano-plastics (MNPs) to the natural environment. Potentially acting as a vector, the role of MNPs on the fate and transport of environmental pollutants (e.g., antibiotics such as chlortetracycline hydrochloride; CTC) has garnered global concern recently. Herein, the cotransport of MNPs and CTC in columns packed with uncoated sand or soil colloid-coated sand (SCCS) under different degrees of physicochemical heterogeneity and ionic strength was systematically explored. Our results show that MNPs and CTC inhibit the transport of each other when they coexist. The adsorption of CTC onto sand grains, soil colloids, and MNPs, as well as the aggregation of MNPs in the presence of CTC could be the major contributors to the enhanced retention of CTC and MNPs. In SCCS with different degrees of soil colloid coating, the adsorption of CTC on soil colloids is critical to influence the transport of CTC, and the nonlinear retention of MNPs to soil colloids is mainly attributed to the alteration of collector surface roughness by soil colloids. High ionic strength slightly facilitates CTC transport due to the competition for adsorption sites and the formation of CTC macromolecules, but significantly inhibits MNPs transport by suppressing the electrostatic double layers based on colloid stability theory. Consequently, the cotransport of MNPs and CTC is governed by the coupled interplay of collector surface roughness and chemical heterogeneity, due to the soil colloid coatings and the adsorbed CTC on the surfaces associated with solution chemistries such as ionic strength. Increased cotransport of MNPs and CTC occurred under a higher concentration of MNPs due to a larger number of adsorption sites for CTC. Our findings advance the current understanding of the complex cotransport of MNPs and antibiotics in the environment. This information is valuable for understanding contaminant fate and formulating strategies for environmental remediation due to the contamination of MNPs and co-occurring contaminants.