Cationic Pollutants Research Articles

One-step removal of anionic/cationic heavy metal ions from wastewater by magnetic amphoteric adsorbent

Simultaneous treatment of wastewater containing anionic and cationic pollutants in an easy-to-operate and environmentally friendly manner is a formidable challenge in environmental remediation. This work designed a low-cost and high-efficient amphoteric adsorbent Fe3O4/Mg-Al LDOs/AlS (SMA) for the simultaneous removal of Cr (VI) and Cu (II) pollutants from wastewater in one step. SMA is prepared with waterworks aluminum-containing sludge (AlS) from typical municipal engineering waste as the base material and loaded with magnetic nanoparticles to enhance recycling process after adsorption. SMA exhibits large specific surface area (∼418 m2/g), thereby providing sufficient adsorption active sites. Adsorption studies indicate that the adsorption of SMA toward two pollutants conforms to the pseudo-second-order kinetic model, while the Langmuir model is used to simulate the adsorption isotherm. The maximum adsorption capacity is calculated to be 235.3 mg/g for Cr (VI) and 669.2 mg/g for Cu (II). Thermodynamic studies reveal the process's spontaneous nature. The main adsorption mechanisms involve electrostatic attraction, surface complexation, isomorphic replacement, and chemical precipitation. Notably, SMA exhibits excellent adsorption performance in a wide pH range and water system containing multiple anions and cations. Moreover, the strong magnetic property facilitates easy separation and recovery through an external magnetic field, maintaining stable adsorption performance even after five cycles. Therefore, this study provides a win-win strategy for promoting environmental safety, not only proposing feasible approaches for the high value-added utilization of waste sludge, but also efficiently addressing the purification problem of complex anionic and cationic coexisting wastewater.

Engineered Fe3 Triangle for The Rapid and Selective Removal of Aromatic Cationic Pollutants

Heydays, water pollution is proliferating due to widespread industrialization and in- proper planning of its waste, consisting of aromatic hazards [1]. Most industries dispose of the wastewater in their neighborhood areas of the cities, which is directly in touch with several groundwater sources. The wastewater pollutant (specialties the aromatic ones) can easily enter the underground water which in turn contaminants the surface water and consequently harm the human and environment [2-5].

Comparison of rhodamine B adsorption and desorption on the aged non-degradable and degradable microplastics: Effects of charge-assisted hydrogen bond and underline mechanism

The accumulation of microplastics (MPs) in the environment and their role as carriers for ionic organic pollutants are increasingly attracting attention. This study evaluated the adsorption-desorption characteristics of the cationic organic pollutant on virgin and UV-aged non-degradable polystyrene (PS) as well as degradable poly(butylene succinate) (PBS) and poly(butylene adipate-co-terephthalate) (PBAT) MPs. The results showed that aging treatment made the surface of MPs rougher and more porous, causing the adsorption to shift from monolayer to multilayer adsorption. Aging increased the oxygen-containing groups on MPs, significantly enhancing the H bond (HB) donor capabilities of degradable aged PBS and PBAT, thereby improving adsorption by more than 10 times. This significant increase in adsorption is mainly due to the combined effects of strong HB (including ordinary HB (OHB) and charge-assisted HB (CAHB)), electrostatic interactions, and π-π interactions. Notably, the stronger HB enabled aged PBS and PBAT to achieve efficient and stable adsorption of rhodamine B over a wide pH range, with significant desorption hysteresis (HI > 1.80). This indicates that degradable aged MPs can act as carriers for long-distance pollutant transport. The significant total desorption of cationic pollutants from aged PBS and PBAT in simulated animal gastrointestinal fluids confirmed the greater environmental hazards of degradable aged MPs. This work is the first to demonstrate that degradable aged MPs, as unique HB donors, can primarily adsorb ionic organic pollutants through strong HB (CAHB and OHB), which helps assess the environmental fate of biodegradable microplastics and pollutants in aquatic systems.

Boosting sunlight driven photocatalytic and catalytic performance of ZnFe2O4-ZnO nanohybrids by loading Ag nanoparticles

We report facile fabrication of magnetically separable Ag@ZnFe2O4-ZnO plasmonic hybrid nanostructures by a simple wet chemical route combined with cost-effective photodeposition. The successful formation of Ag@ZnFe2O4-ZnO hybrid nanostructures was confirmed using XRD, Raman, FESEM, TEM, HRTEM and SAED characterizations. The catalytic and photocatalytic capabilities of the synthesized magnetic Ag@ZnFe2O4-ZnO plasmonic hybrid nanostructures were evaluated with regard to 4-NP to 4-AP reduction in dark and photodecomposition of major anionic and cationic pollutants (MB, MG, MO, RhB) and emerging pollutant levofloxacin antibiotic under sunlight illumination, respectively. Results showed that Ag@ZnFe2O4-ZnO hybrid nanostructures exhibit excellent catalytic as well as photocatalytic response and reduced 98.1 % of 4-NP in only 6 min and decolorized 92.9, 93, 43.4 and 73.3 % of MB, MG, MO and RhB within only 18 min and 90.5 % of levofloxacin in 40 min of sun light irradiation, respectively. Further, the synthesized nanohybrids possess high stability and can be magnetically recovered due to its good magnetic response. In addition, the trapping experiments indicated that the main active compounds for the photodegradation of dyes are OH radicals. We demonstrate that the prepared Ag@ZnFe2O4-ZnO plasmonic hybrid nanostructures have potential application towards decomposition of organic pollutants and other emerging pollutants in wastewater for environmental remediation.

Remarkably Enhanced Phosphate Sequestration from Waters by Biochar with High-Density Quaternary Ammonium Groups.

A new biochar (N-BC) was fabricated by incorporating high-density positively charged quaternary ammonium groups into the pristine biochar without any adsorption for phosphate. N-BC can highly efficiently remove phosphate with an optimal pH of 5.0, a maximum experimental adsorption capacity of 30 mg of P/g, and an adsorption equilibrium time of 180 min. The predicted pore diffusion coefficient D (the diffused surface area of the adsorbate for unit time) for phosphate adsorption by N-BC was 5.3 × 10-9 cm2/s. N-BC can still capture phosphate in the copresence of anion Cl- with a molar concentration 50 times that of phosphate. The exhausted N-BC was completely regenerated using a 10 wt % NaOH solution and further reused without any observable loss in adsorption capacity. Moreover, N-BC yielded ∼324 bed volumes (BV) of wastewater containing 1 mg P/L phosphate and 50 mg/L Cl- before breakthrough occurring (<0.1 mg P/L in effluent) in a fixed-bed column operation system. The introduced quaternary ammonium groups covalently bound to biochar played a dominant role in phosphate sequestration by N-BC through forming the out-sphere complexation with phosphate. All results imply that it is of promising prospect for N-BC practical application for phosphate purification from waters. The present study provided a new strategy to expand the application of biochar, usually serving as an adsorbent for cationic pollutants, to the purification of anionic pollutants such as phosphate from waters.

Enhanced Adsorption of Methylene Blue Dye on Functionalized Multi-Walled Carbon Nanotubes.

Carbon nanomaterials are promising adsorbents for dye removal from wastewater also due to their possible surface functionalization that, in principle, can increase the adsorption rate and provide regeneration. To investigate the real advantages of functionalization, we synthesized and characterized through IR, TGA, TEM, XPS and DLS measurements a multi-walled carbon nanotube (MWCNT) derivative bearing benzenesulfonate groups (MWCNT-S). The obtained material demonstrated to have good dispersibility in water and better capability to adsorb methylene blue (MB) compared to the pristine MWCNT adsorbent. Adsorption kinetic studies showed a very fast process, with a constant significantly higher with respect not only to that of the unfunctionalized MWCNT adsorbent but also to those of widely used activated carbons. Moreover, the adsorption capacity of MWCNT-S is more than doubled with respect to that of the insoluble pristine MWCNT adsorbent, thanks to the dispersibility of the derivatives, providing a larger available surface, and to the possible electrostatic interactions between the cationic MB and the anionic sulfonate groups. Additionally, the reversibility of ionic interactions disclosed the possibility to release the adsorbed cationic pollutant through competition with salts, not only regenerating the adsorbent, but also recovering the dye. Indeed, by treating the adsorbed material for 1 h with 1 M NaCl, a regeneration capacity of 75% was obtained, demonstrating the validity of this strategy.

Boosted electrostatic interaction by surface sulfonation over Calixarene-TPE copolymer for prompt adsorption of cationic contaminates

Removal of cationic pollutants, including dyes, herbicides, and antibiotics from water is significant owing to their persistence, bioaccumulation, carcinogenicity, mutagenicity, and reproductive risks. In this paper, a calixarene-tetraphenyl ethylene containing copolymer adsorbent, named CP-TPE, was synthesized using the Suzuki-Miyaura coupling reaction between the resorcinol calixarene and tetraphenyl ethylene boric acid esters. Subsequently, the phenolic groups on the CP-TPE were further reacted with chlorosulfonic acid, resulting in a sulfonated product named CP-TPE-SO3H. The introduction of the sulfonate groups not only significantly improved the hydrophilicity of CP-TPE-SO3H but also enhanced the electrostatic interaction between CP-TPE-SO3H and cationic molecules, achieving an outstanding maximum adsorption capacity for paraquat (representative herbicide, 300.06 mg g−1) and tetracycline hydrochloride (representative antibiotic, 888.74 mg g−1), which surpassed the majority of reported polymeric adsorbents. Moreover, the k2 of CP-TPE-SO3H on TC (0.0407 g mg−1 min−1) reached the maximum value reported so far. This study demonstrated the significance and superiority of sulfonation modification in synthesizing POPs-based adsorbents, which can be potentially employed in real wastewater treatment.

Harnessing a Ti-based MOF for selective adsorption and visible-light-driven water remediation.

In pursuit of universal access to clean water, photocatalytic water remediation using metal-organic frameworks (MOFs) emerges as a strong alternative to the current wastewater treatment methods. In this study, we explore a unique Ti-based MOF comprised of 2D secondary-building units (SBUs) connected via biphenyl dicarboxylic acid (H2bpdc) ligands - denoted as COK-47 - as a visible-light-driven photocatalyst for organic dye degradation. Synthesized via a recently developed microwave-assisted method, COK-47 exhibits high hydrolytic stability, demonstrates a strong dye uptake, and shows noteworthy dye-degradation performance under UV, visible, and solar light, outperforming benchmark TiO2 and MIL-125-Ti photocatalysts. Due to its nanocrystalline structure and surface termination with organic linkers, COK-47 exhibits selective degradation of cationic pollutants while remaining inert towards anionic dyes, thus highlighting its potential for selective oxidation reactions. Mechanistic studies reveal the involvement of superoxide radicals in the degradation process and emphasize the need to minimize the recombination of photogenerated electron-hole pairs to achieve optimal performance. Post-catalytic studies further confirm the high stability and reusability of COK-47, making it a promising photocatalyst for water purification, organic transformation, and water splitting reactions under visible light.

Tuning of surface oxygen vacancies for enhancing photocatalytic performance under visible light irradiation in Sb2WO6 nanostructures.

Tuning of vacancies in photocatalytic materials has emerged as a versatile strategy to enhance visible light absorption and photocatalytic activity. In this study, surface oxygen vacancies (defects) were incorporated on antimony tungstate to boost its photocatalytic activity, which was examined by studying the degradation of model pollutants under visible light irradiation. Specifically, a two-to-three-fold increase in photocatalytic activity was observed for oxygen vacancy-rich antimony tungstate in comparison to its pristine counterpart. This improvement in the photocatalytic performance can be attributed to the presence of oxygen vacancies in the material, which leads to an enhanced absorption of light, decrease in the recombination of charge carriers, and increase in the number of active sites. In addition, owing to the nature of the surface charge present, the photocatalysts were found to be selective for the degradation of cationic pollutants in comparison to anionic and neutral pollutants, and can thus be used for the separation of a mixture of pollutants. Furthermore, scavenger studies illustrate that holes play a major role in the photocatalytic degradation of pollutants. Moreover, the excellent photostability of oxygen vacancy-rich antimony tungstate over three consecutive cycles demonstrates its potential as a good photocatalyst for the degradation of pollutants. Overall, this study demonstrates that the engineering of surface vacancies on perovskite oxide materials can render them as efficient single component photocatalysts for environmental remediation applications.

Hydrothermal carbonization of Calotropis procera leaves as a biomass: Preparation and characterization

Hydrothermal carbonization (HTC) is a biowaste treatment process and a promising technology for many applications. The use of Calotropis procera (CP), found in the Egyptian desert, as a biosource feedstock for the HTC process. In the present work, different process conditions were applied during the HTC process. The influence of temperature, time, and particle size was studied to produce hydrochar using CP leaves as biomass. The hydrochar samples were characterized by many analytical techniques. The temperature and time controlled the severity of the reaction; they caused a significant decrease in the yield (wt.%) and caused an increase in the carbon content of the hydrochar product, with a value of 57.03 % at 240 °C and a time of 180 min. Although time in this case has a more significant effect than temperature, a long reaction time influences the hydrochar yield. FTIR showed the formation on hydrochar with high content of lignin at high temperature and longtime. The O/C decrease with increase the temperature and time as evidence of decarboxylation reaction occurs and the reaction move toward carbonization and increase the HHV of hydrochar than raw biomass that recorded 40.2 MJ/Kg at 240 °C, time 180 min and biomass particle size 150 μm. The hydrochars produced under all condition have negative surface charge in wide range of pH and all have negative charge over pH 4–5 and most suitable pH value is between 6 and 7. The best conditions recorded were temperature 200–240 °C and reaction time 120–180 min at this conditions hydrochar has a stable negative charge in slightly acidic and basic media which let it able to use in applications of removing the cationic pollutants from wastewater, and the high heating value give opportunity to use in energy production applications.

Removal of cationic dyes from aqueous solution using polyacrylic acid modified hemp stem.

Water pollution caused by dyes is a pressing environmental challenge due to their persistence and difficulty in degradation. Herein, an anionic adsorbent (HS-PAANa) was synthesized by grafting polyacrylic acid (PAA) onto the agricultural waste-hemp stem (HS). The obtained HS-PAANa adsorbent exhibited rapid adsorption kinetics, high adsorption capacity, and a favorable preference for cationic dyes, such as methylene blue (MB) and crystal violet (CV). The experimental data fit well with the pseudo-second-order kinetic model and Langmuir isotherm, demonstrating the efficiency of HS-PAANa in dye removal. Notably, the optimal adsorption capacities of HS-PAANa for MB and CV were found to be 1296.65 mg/g and 1451.43 mg/g, respectively. In the cationic/anionic dyes (MB/MO) binary systems, HS-PAANa exhibited enhanced selective adsorption of cationic dyes (MB), indicating its potential for targeted removal of specific dyes from mixed solutions. Moreover, HS-PAANa adsorption shows an excellent recyclability, after five cycles, HS-PAANa still maintained MB and CV removal rates of 93.85% and 95.08%, respectively. Therefore, the bioadsorbent HS-PAANa exhibits high potential as a highly efficient adsorbent for the effective treatment of cationic pollutants in wastewater.

Enhancing performance of rubber mortar and water pollutant capture via fast and facile modification of recycled waste rubber particles

A fast, facile and highly efficient approach was developed in this study for the modification of recycled rubber particles (RP) into modified rubber particles (RP-TA-Fe3+). The incorporation of RP-TA-Fe3+ in cement-based materials effectively counteracted the detrimental effects typically associated with rubber. The TA-Fe3+ metal phenolic network proficiently impeded the leaching of heavy metal ions from the modified rubber and also effectively adsorbed cationic pollutants (MB and Cu2+) from water. The experimental results revealed that the rubber mortar containing RP-TA-Fe3+ exhibited reduced porosity and significantly improved flexural and compressive strength compared to the rubber mortar containing RP. Furthermore, the incorporation of RP-TA-Fe3+ into cement-based materials markedly enhanced their adsorption capabilities for MB and Cu2+.

Novel rod-like [Cu(phen)2(OAc)]·PF6 complex for high-performance visible-light-driven photocatalytic degradation of hazardous organic dyes: DFT approach, Hirshfeld and fingerprint plot analysis

A novel octahedral distorted coordination complex was formed from a copper transition metal with a bidentate ligand (1,10-Phenanthroline) and characterized by Ultraviolet–visible spectroscopy, Ultraviolet–visible diffuse reflectance spectroscopy, Fourier-transform infrared spectroscopy, Brunauer-Emmett-Teller, Field emission scanning electron microscopy, and Single-crystal X-ray diffraction. The Hirshfeld surface and fingerprint plot analyses were conducted to determine the interactions between atoms in the Cu(II) complex. DFT calculations showed that the central copper ion and its coordinated atoms have an octahedral geometry. The Molecular electrostatic potential (MEP) map indicated that the copper (II) complex is an electrophilic compound that can interact with negatively charged macromolecules. The HOMO-LUMO analysis demonstrated the π nature charge transfer from acetate to phenanthroline. The band gap of [Cu(phen)2(OAc)]·PF6 photocatalyst was estimated to be 2.88 eV, confirming that this complex is suitable for environmental remediation. The photocatalytic degradation of erythrosine, malachite green, methylene blue, and Eriochrome Black T as model organic pollutants using the prepared complex was investigated under visible light. The [Cu(phen)2(OAc)]·PF6 photocatalyst exhibited degradation 94.7, 90.1, 82.7, and 74.3 % of malachite green, methylene blue, erythrosine, and Eriochrome Black T, respectively, under visible illumination within 70 min. The results from the Langmuir-Hinshelwood kinetic analysis demonstrated that the Cu(II) complex has a higher efficiency for the degradation of cationic pollutants than the anionic ones. This was attributed to surface charge attraction between photocatalyst and cationic dyes promoting removal efficiency. The reusability test indicated that the photocatalyst could be utilized in seven consecutive photocatalytic degradation cycles with an insignificant decrease in efficiency.

Sustainable and efficient extraction of lignin from wood meal using a deep eutectic system and adsorption of neutral red dye with the extraction residue

In this study, the efficient extraction of lignin from wood meal using a deep eutectic system (DESys) was explored, and the obtained lignin was characterized. The impact of various factors, such as the type of DESys components, extraction time, temperature, water content, and solid-liquid ratio, on the lignin extraction process was systematically investigated. The results indicated that a DESys with a carboxylic acid as the HBD provided the highest lignin extraction efficiency. The obtained lignin was characterized in terms of its molecular weight distribution, elemental composition, functional groups, crystalline structure, and thermal stability. The results showed that the lignin obtained by DESys-based extraction had similar properties to lignin extracted using traditional method. Additionally, the study examined the utilization of the residue left after lignin extraction for the adsorption of cationic pollutants, such as the cationic dye neutral red (NR). The residue was found to contain carboxyl groups, which enabled it to adsorb NR efficiently. The kinetic and thermodynamic models suggested that the adsorption was a chemisorption process. Furthermore, the residue showed selective adsorption for cationic dye over anionic dye. This selectivity was attributed to interactions between the residue's functional groups and the cationic dye molecule. Overall, this study provided a sustainable and comprehensive approach to lignin extraction from lignocellulosic biomass using DESys. It also demonstrated the potential of using the residue from the extraction process for the removal of cationic pollutants from wastewater, showcasing a multi-faceted approach to the valorization of lignocellulosic materials.

Synthesis of zeolite and aluminum-modified zeolite from lake sediment for simultaneous immobilization of cationic and anionic pollutants in lakes

Aiming at the development of ecologically safe and environmentally friendly materials to immobilize both anionic and cationic pollutants in eutrophic lakes, we have attempted to synthesize zeolites and aluminum-modified zeolites (AMZs) from four lake sediments by a fusion-assisted hydrothermal method. Characterization by X-ray fluorescence spectrometry, X-ray diffraction analysis, Fourier-transform infrared spectrometry, scanning electron microscopy, and specific surface area measurements confirmed that zeolites including Na–X, Na–P1, and hydroxysodalite were successfully synthesized, and the AMZs composed of zeolite and amorphous hydrous aluminum oxide were formed. The cation-exchange capacity (representing the ability to adsorb cationic pollutants) and the phosphate adsorptive capacity (representing the ability to adsorb anionic pollutants) of zeolites (204.3–305.7 cmol/kg and 9.3–16.3 mgP/g, respectively) and AMZs (105.7–309.2 cmol/kg and 26.8–38.9 mgP/g, respectively) were much higher than those of the original lake sediments (3.7–6.4 cmol/kg and 0.5–1.7 mgP/g, respectively). Incubation of sediment in lake water under anoxic conditions, which are commonly encountered at the beds of eutrophic lakes, triggered substantial release of phosphorus, iron, manganese, and ammonium, but amendment with AMZ significantly reduced the concentrations of these pollutants in the overlying water. Our findings demonstrated that zeolite and AMZ synthesized from lake sediments may be applied as suitable materials for the remediation of eutrophic lakes.

Anchoring modified g-C3N4 with Bi5O7Br: S-scheme photocatalysts with boosted activities in elimination of inorganic and organic pollutants

In this research, modified g-C3N4 with hydrogen peroxide was decorated with Bi5O7Br nanoparticles (abbreviated as g-C3N4(M)/Bi5O7Br) via a facile precipitation procedure. The s-scheme g-C3N4(M)/Bi5O7Br (20 %) nanocomposite showed superior photocatalytic ability in degradation to tetracycline (TC), as a pharmaceutical pollutant, upon visible light. The maximal removal constant was 34.3 and 6.83-folds premier than g-C3N4 and g-C3N4 (M) systems, respectively. Interestingly, the g-C3N4(M)/Bi5O7Br (20 %) nanocomposite demonstrated excellent activity in visible-light elimination of amoxicillin (AMX) (an antibiotic), methyl orange (an anionic pollutant), rhodamine B and Fuchsine (cationic pollutants), and also photoconversion of Cr (VI) into Cr (III) upon visible light, that was about 15.5, 18.9, 22.4, 21.7, and 23.2-folds preferable than that of g-C3N4, respectively. The spectrophotometric, photoluminescence, and electrochemical studies approved the production of more charges upon visible light, and promoted segregation/movement of the generated charges within the binary g-C3N4(M)/Bi5O7Br (20 %) photocatalyst. The impressive segregation of charges was assigned to developing an s-scheme structure between Bi5O7Br and g-C3N4 (M) semiconductors. Scavenging tests revealed that superoxide anion radicals, holes, and hydroxide radicals were crucial species in the reactions. Eventually, the biocompatibility of the treated solution was confirmed via the successful growth of wheat seeds. In conclusion, the s-scheme g-C3N4(M)/Bi5O7Br system can be used as a suitable sample for environmental detoxification.

Trithiocyanurate-functionalized hydrochar for effectively removing methylene blue and Pb (II) cationic pollutants

Functionalization can change the physicochemical properties of hydrochar and improve its ability to adsorb pollutants. Herein, a trithiocyanurate-functionalized hydrochar (TTHC) was obtained from acylation of chloroacetyl chloride and hydrochar and modification with trithiocyanuric acid in alkaline conditions. TTHC can efficiently remove cationic methylene blue (MB) and Pb(II) from wastewater. The removal can be expressed with pseudo-second-order kinetic and Langmuir models. The MB and Pb(II) removed uptakes by TTHC at 298 K exceeded 909.9 and 182.8 mg g−1 respectively, and the removal rates reached 90% and 98% within 120 min respectively. Characterizations show TTHC is functionalized with trithiocyanurate, and rich in thiolate and aromaticity, and tends to adsorb MB/Pb(II) via multiple adsorption mechanisms. After five sorption-desorption regeneration cycles, TTHC maintained 80% and 99% adsorption capacities for MB and Pb(II) respectively. Therefore, TTHC is a promising efficient sorbent for removing MB and Pb(II) from effluents.

Highly sensitive detection of cationic pollutants on molybdenum carbide (MXene)/Fe2O3/Ag as a SERS substrate

Recent studies reported that the two-dimensional transition-metal carbides (MXenes) present promising results for surface-enhanced Raman spectroscopy (SERS) application, permitting sensitive detection of analyte molecules thanks to rich surface chemistries, surface plasmon resonances, and electrical features. However, Mxene materials, especially Mo-based ones, still suffer from low concentrated sensing activity and lack specific sensing suited to surface chemistries. To overcome those issues, for the first time, we propose a simple and scalable approach to fabricate Mo2CTx/Fe2O3/Ag (MFA) hybrid nanostructure via the hydrothermal treatment of MXene and Fe2O3, and subsequent in-situ decorated of Ag NPs via seed-mediated growth processes. As-prepared MFA presents a 1 × 10−9 M detection limit with a 1.46 × 106 enhancement factor for cationic MB molecules. Here, in addition to the contribution of the electromagnetic enhancement mechanism due to the presence of Ag, the chemical enhancement mechanism also comes into play as a result of the specific binding of the cationic molecule, MB, to the negatively charged MXene surface. This result is also observed for harmful cationic molecules found in wastewater such as CTAC and arsenic. MFA exhibits a low detection limit for CTAB, where a very low concentration of 0.075 M was achieved probably owing to its cationic character. Last but not least, the MFA hybrid nanostructure shows promising results for arsenic detection in tap water with 10 μg/L. Overall, an as-prepared MFA is a promising option for creating a SERS-active surface that can be customized for particular uses, due to its adjustable surface chemistries and elevated charge carrier densities, while also being low-cost and simple to manufacture.

Mechanistic insight and optimisation of hydrothermally pre-treated biowaste-derived biochar for saline water treatment

The valorisation of oil palm empty fruit bunch is challenging due to its poor surface functionalities, which require a comprehensive pre-treatment process. To ensure efficient valorisation of the agricultural waste, the biochar derived from empty fruit bunch is subjected to hydrothermal nitric acid pre-treatment to act as an adsorbent for sodium ions removal from the saline solution. For this newly developed adsorbent, the adsorption study provides important information on the adsorption behaviour of sodium ions and the optimum conditions for sodium ions removal, which is crucial for effective process design and operation control during practical applications. Physicochemical characterisation revealed the successful adsorption of sodium ions by Hydrothermal Nitric acid Pre-treated EFB Biochar (HNO3 EFB-BC. The highest sodium ions removal efficiency of HNO3 EFB-BC (92.04%) was achieved under the optimum reaction conditions: 0.39 M initial concentration of the saline solution, 4.96 g of HNO3 EFB-BC, contact time of 17.4 h and solution pH of 7.46. Upon process optimisation, the adsorption capacity of HNO3 EFB-BC towards sodium ions improved remarkably (p < 0.05) from 78.34 mg g-1 to 166.45 mg g-1. The adsorption isotherm and kinetic study are consistent with the Langmuir and pseudo-second-order models, implying a monolayer chemisorption-dominated adsorption process. The promising sodium ions adsorption capacity of HNO3 EFB-BC can be attributed to the enhanced surface functionalities of the adsorbent. The molecular modelling using the density functional theory approach has successfully identified the nitro group as the most favourable functional group in producing the charges sites for sodium ions adsorption, with the most stable reaction route between HNO3 EFB-BC and sodium ions being identified. This study highlighted the density functional theory approach as a tool for identifying the specific functional groups with enhanced adsorption capability for saline water treatment and provides a reference value for removing sodium ions in the presence of other cationic pollutants.

Superfast removal of dyes and herbicides with triphenylamine-based porous organic polymers by one-step sulfonation and carboxylation

The water pollution caused by modern chemical industries has become one of the most severe global environmental challenges, as an effective approach, the development of cost-effective adsorbents with rapid removal efficiency is of great significance. Herein, a simple and cost-effective post-modification synthetic strategy that includes sulfonation and carboxylation for the synthesis of porous organic polymer (POP-SO3H) was proposed, which endows POP-SO3H ultrafast adsorption rates, high adsorption capacity, and excellent reusability. For cationic dyes and herbicides including methylene blue (MB), rhodamine B (RhB), paraquat, and diquat, the removal efficiencies of POP-SO3H all reached > 96 % in only 10 s interaction and reached equilibrium within 30 s. The uptake kinetics of MB, RhB, paraquat, and diquat are 17.29, 16.12, 25.14, and 60.96 g mg−1 min−1, respectively, outperforming most of the previously reported adsorbents. Moreover, the removal efficiencies of flow-through experiments towards MB and RhB still remained > 99 % even at the flow rate of 14.7 mL min−1. This study provides a ‘one stone with two birds’ post-functionalization strategy for the preparation of cost-effective anionic adsorbents with superfast removal kinetics toward cationic pollutants.