Adsorptive removal of PPCPs from aqueous solution using carbon-based composites: A review

Exploring the potential of eco-friendly carbon dots in monitoring and remediation of environmental pollutants

Photoluminescent carbon dots (CDs) have garnered significant interest owing to their distinctive optical and electronic properties. In contrast to semiconductor quantum dots, which incorporated toxic elements in their composition, CDs have emerged as a promising alternative, rendering them suitable for both environmental and biological applications. CDs exhibit astonishing features, including photoluminescence, charge transfer, quantum confinement effect, and biocompatibility. Recently, CDs derived from green sources have drawn a lot of attention due to their strong photostability, reduced toxicity, better biocompatibility, enhanced fluorescence, and simplicity. These attributes have shown great promise in the areas of LED technology, bioimaging, photocatalysis, drug delivery, biosensing, and antibacterial activity. In contrast, this review offers a comprehensive overview of various green sources utilized to produce CDs and methodologies, along with their merits and demerits, with a notable emphasis on physiochemical properties. Additionally, the paper provides insight into the bibliometric analysis and recent advancements of CDs in sensing, photocatalysis, and antibacterial activity. In this field, extensive research is underway, and a total of 7,438 articles have been identified. Among these, 4242 articles are dedicated to sensing applications, while 1518 and 1678 focus on adsorption and degradation. Carbon dots demonstrate exceptional sensing capabilities within the nanomolar range with a selectivity of up to 95% for pollutants. They exhibit excellent degradation efficiency exceeding 90% within 10-130 min and possess an adsorption capacity from 100 to 800 mg/g. These fascinating qualities render them suitable for diverse applications.

Nitrogen-doped mesoporous activated carbon from Lentinus edodes residue: an optimized adsorbent for pharmaceuticals in aqueous solutions

In this study, phosphoric acid activation was employed to synthesize nitrogen-doped mesoporous activated carbon (designated as MR1) from Lentinus edodes (shiitake mushroom) residue, while aiming to efficiently remove acetaminophen (APAP), carbamazepine (CBZ), and metronidazole (MNZ) from aqueous solutions. We characterized the physicochemical properties of the produced adsorbents using scanning electron microscopy (SEM), nitrogen adsorption isotherms, and X-ray photoelectron spectroscopy (XPS). MR1, MR2, and MR3 were prepared using phosphoric acid impregnation ratios of 1, 2, and 3 mL/g, respectively. Notably, MR1 exhibited a significant mesoporous structure with a volume of 0.825 cm3/g and a quaternary nitrogen content of 2.6%. This endowed MR1 with a high adsorption capacity for APAP, CBZ, and MNZ, positioning it as a promising candidate for water purification applications. The adsorption behavior of the contaminants followed the Freundlich isotherm model, suggesting a multilayer adsorption process. Notably, MR1 showed excellent durability and recyclability, maintaining 95% of its initial adsorption efficiency after five regeneration cycles and indicating its potential for sustainable use in water treatment processes.

Predicting the removal efficiency of pharmaceutical and personal care products using heated metal oxides as adsorbents based on their physicochemical characteristics

Pharmaceutical and personal care products (PPCPs) are emerging pollutants that are commonly found in the environment and exist predominantly in nondegradable forms. Several attempts have been made to remove PPCPs via conventional wastewater treatment processes; however, these processes have limitations, such as high costs and insufficient removal efficiencies. Adsorption is a promising alternative for removing PPCPs because it is inexpensive, highly reusable, and easy to operate. Therefore, this study aims to determine the contributing characteristics that can be used to predict the adsorption behaviour of PPCPs based on their physicochemical properties, with heated metal oxide adsorbents (HMOAs). HAOP (heated aluminium oxide particles) and HIOP (heated iron oxide particles) with particle sizes below 38 μm were used. Results from the Brunauer-Emmett-Teller (BET) analysis show that HIOP has higher surface area and smaller pore size (113.7 ± 26.3 m2/g and 5.4 ± 1.8 nm) than HAOP (14.5 ± 0.6 m2/g and 18.6 ± 3.1 nm), which suggest that HIOP would show superior adsorption rates compared to HAOP. The adsorption mechanism is identified based on three major physicochemical properties of PPCPs: molecular weight (M.W.), octanol-water partition coefficient (log Kow), and acid dissociation constant (pKa). The results suggest that the most dominant factor that contributes to the adsorption of PPCPs on to HMOAs is the M.W., where the larger the molecular size, the better the adsorption efficiency. The tests conducted with varying log Kow values revealed that the hydrophilicity of the adsorbent influences the adsorption performance. It was found that HIOP exhibits better removal efficiencies with hydrophilic PPCPs (up to 83%) than with hydrophobic PPCPs (48%), while HAOP exhibits better removal efficiencies with hydrophobic PPCPs (86%) than with hydrophilic PPCPs, with less than 10% removal. Unlike the M.W. and pKa values, the log Kow does not exhibit any visible trend. Therefore, the adsorption behaviour can be predicted with the M.W. and pKa values of the PPCPs, when HAOP and HIOP are used as adsorbents.

Sulfonated polyhedral oligomeric silsesquioxane-cyclodextrin hybrid polymers for efficient removal of micropollutants from water

Herein, β-cyclodextrin-containing hybrid polymers (P1, P2 and P3) were prepared through crosslinking partially benzylated β-cyclodextrin (PBCD) by octavinylsilsesquioxane (OVS). P1 stood out in screening studies and the residual hydroxyl groups of PBCD was sulfonate-functionalized. The obtained P1-SO₃Na showed greatly enhanced adsorption towards cationic MPs and maintained the excellent adsorption performance towards neutral MPs. The rate constants (k₂) of cationic MPs upon P1-SO₃Na were 9.8-34.8 times larger than those upon P1. The equilibrium uptakes of the neutral and cationic MPs upon P1-SO₃Na were above 94.5 %. Meanwhile, P1-SO₃Na demonstrated appreciable adsorption capacities, excellent selectivity, effective adsorption of mixed MPs at environmental levels and good reusability. These results confirmed the great potential of P1-SO₃Na as effective adsorbent to remove MPs from water.

Three-dimensional heterogeneous electro-Fenton system with reduced graphene oxide based particle electrode for Acyclovir removal

New pollutant pharmaceutical and personal care products (PPCPs), especially antiviral drugs, have received increasing attention not only due to their increase in usage after the outbreak of COVID-19 epidemics but also due to their adverse impacts on water ecological environment. Electro-Fenton technology is an effective method to remove PPCPs from water. Novel particle electrodes (MMT/rGO/Fe₃O₄) were synthesized by depositing Fe₃O₄ nanoparticles on reduced graphene oxide modified montmorillonite and acted as catalysts to promote oxidation performance in a three-dimensional Electro-Fenton (3D-EF) system. The electrodes combined the catalytic property of Fe₃O₄, hydrophilicity of montmorillonite and electrical conductivity of graphene oxides, and applied for the degradation of Acyclovir (ACV) with high efficiency and ease of operation. At optimal condition, the degradation rate of ACV reached 100% within 120 min, and the applicable pH range could be 3 to 11 in the 3D-EF system. The stability and reusability of MMT/rGO/Fe₃O₄ particle electrodes were also studied, the removal rate of ACV remained at 92% after 10 cycles, which was just slightly lower than that of the first cycle. Potential degradation mechanisms were also proposed by methanol quenching tests and FT-ICR-MS.

Alkyl chain length of quaternized SBA-15 and solution conditions determine hydrophobic and electrostatic interactions for carbamazepine adsorption

Santa Barbara Amorphous-15 (SBA) is a stable and mesoporous silica material. Quaternized SBA-15 with alkyl chains (Q_SBA) exhibits electrostatic attraction for anionic molecules via the N⁺ moiety of the ammonium group, whereas its alkyl chain length determines its hydrophobic interactions. In this study, Q_SBA with different alkyl chain lengths were synthesized using the trimethyl, dimethyloctyl, and dimethyoctadecyl groups (C1Q_SBA, C8Q_SBA, and C18Q_SBA, respectively). Carbamazepine (CBZ) is a widely prescribed pharmaceutical compound, but is difficult to remove using conventional water treatments. The CBZ adsorption characteristics of Q_SBA were examined to determine its adsorption mechanism by changing the alkyl chain length and solution conditions (pH and ionic strength). A longer alkyl chain resulted in slower adsorption (up to 120 min), while the amount of CBZ adsorbed was higher for longer alkyl chains per unit mass of Q_SBA at equilibrium. The maximum adsorption capacities of C1Q_SBA, C8Q_SBA, and C18Q_SBA, were 3.14, 6.56, and 24.5 mg/g, respectively, as obtained using the Langmuir model. For the tested initial CBZ concentrations (2-100 mg/L), the adsorption capacity increased with increasing alkyl chain length. Because CBZ does not dissociate readily (pK_a = 13.9), stable hydrophobic adsorption was observed despite the changes in pH (0.41-0.92, 1.70-2.24, and 7.56-9.10 mg/g for C1Q_SBA, C8Q_SBA, and C18Q_SBA, respectively); the exception was pH 2. Increasing the ionic strength from 0.1 to 100 mM enhanced the adsorption capacity of C18Q_SBA from 9.27 ± 0.42 to 14.94 ± 0.17 mg/g because the hydrophobic interactions were increased while the electrostatic attraction of the N⁺ was reduced. Thus, the ionic strength was a stronger control factor determining hydrophobic adsorption of CBZ than the solution pH. Based on the changes in hydrophobicity, which depends on the alkyl chain length, it was possible to enhance CBZ adsorption and investigate the adsorption mechanism in detail. Thus, this study aids the development of adsorbents suitable for pharmaceuticals with controlling molecular structure of QSBA and solution conditions.

Rational design of cobalt sulfide anchored on nitrogen-doped carbon derived from cyanobacteria waste enables efficient activation of peroxymonosulfate for organic pollutants oxidation

With the increasing of eutrophication in water body, algae blooms have become one of the global environmental problems. The cyanobacteria waste has placed a severe burden on the environment and transforming cyanobacteria into functional materials may be a wise approach. Herein, cobaltous sulfide/nitrogen-doped biochar (N-BC/CoS_x) composite was synthesized by pyrolysis of cyanobacteria waste. The N-BC/CoS_x showed excellent performance in peroxymonosulfate (PMS) activation for enrofloxacin (ENR) degradation, which could remove more than 90% ENR within 60 min. The influencing factors of pH and catalyst dosage on ENR removal efficiency were studied. The N-BC/CoS_x showed good recyclability in the cycle runs. The radicals (O₂^•-, OH andSO₄^•-) and the non-radical species (charge transfer and ¹O₂) were generated in the ENR degradation. The cycle of Co(II)/Co(III) m ay contribute to the radical generation process. This work proved that metal sulfide modified cyanobacteria biochar has a specific application value in water pollution control and provides a new method for resource utilization of cyanobacteria.

Design strategy of self-assembled BC@MIL-100(Fe) composite membrane for the efficient removal of diclofenac sodium from water

Pharmaceuticals and personal care products (PPCPs) as typical emerging pollutant have attracted extensive attention due to the risks to human health and environment. As a kind of harmful PPCPs, diclofenac sodium (DCF) has been frequently detected in water environment, which needs to be removed effectively. Herein, we successfully fabricated network structure composite membranes consisting of one-dimensional (1D) well-defined core-shell bacterial cellulose (BC)@MIL-100 (Fe) nanofibers by a simple but effective step-by-step strategy. The BC@MIL-100(Fe) composite membrane has three-dimensional network utilizing bacterial cellulose nanofiber as template, which was observed as the MIL-100(Fe) grew on the nanofiber uniformly and obvious core-shell structure. Impressively, the BC@MIL-100(Fe) not only possessed favorable architecture but also behaved good properties to adsorb DCF from water. As we expected, the as-obtained BC@MIL-100(Fe) composite membrane exhibited convenient recycling, high chemical stability, and short equilibrium time (30 min) with high adsorption capacity (296 mg g^-1). Strikingly, in low DCF concentration solution, BC@MIL-100(Fe) composite showed high adsorption efficiency in periodic test, which can still reach 70% after five successive adsorptions without desorption. The results demonstrated that the adsorption mechanism may involve π-π interaction, H-bond interaction, and electrostatic interaction. This work proposes the new finding to understand the removing of DCF from water environment.

Contribution Evaluation of Physical Hole Structure, Hydrogen Bond, and Electrostatic Attraction on Dye Adsorption through Individual Experiments

Disagreements over various unanswered questions about contribution of the adsorption process and functional groups on dye adsorption still exist. The main aim of this research was to evaluate the contributions of physical hole structure, hydrogen bond, and electrostatic attraction on dye adsorption. Three ideal representatives, namely, a sponge with porous structure, P(AM) containing -CONH2 groups, and P(AANa/AM) containing -COONa groups, were chosen to evaluate the above contributions. The methylene blue (MB) removal rates of these three products were compared through individual experiments. The results revealed that physical hole structure did not play a role in decreasing dye concentration. Hydrogen bond existed in dye adsorption but did not remarkably reduce dye concentration. The excellent removal results of P(AANa/AM) demonstrated that electrostatic attraction was critical in enriching dye contaminants from the solution into solid adsorbent. The results could provide insights into the dye adsorption mechanisms for further research.

Molecular Design of the Polyamide Layer Structure of Nanofiltration Membranes by Sacrificing Hydrolyzable Groups toward Enhanced Separation Performance

Nanofiltration (NF) is an effective technology for removing trace organic contaminants (TrOCs), while the inherent trade-off effect between water permeance and solute rejections hinders its widespread application in water treatment. Herein, we propose a novel scheme of "monomers with sacrificial groups" to regulate the microstructure of the polyamide active layer via introducing a hydrolyzable ester group onto piperazine to control the diffusion and interfacial polymerization process. The achieved benefits include narrowing the pore size, improving the interpore connectivity, enhancing the microporosity, and reducing the active layer thickness, which collectively realized the simultaneous improvement of water permeance and enhancement of TrOCs rejection performance. The resulting membranes were superior to both the control and commercial membranes, especially in water-TrOCs selectivity. The effects of using the new monomers on the membrane physicochemical properties were systematically studied, and underlying mechanisms for the enhanced separation performance were further revealed by simulating the polymerization process through density functional theory calculation and measuring the trans-interface diffusion rate of monomers. This study demonstrates a novel promising NF membrane synthesis strategy by designing the structure of reaction monomers for achieving excellent rejection of TrOCs with a low energy input in water treatment.

Kinetic optimization of odor adsorption with acetate fiber cloth prepared from waste cigarette filter

Odor pollution with NH₃ as major contributor is a notorious issue that strongly influences our living environment. NH₃ removal with acetate fiber cloth (AFC) prepared from waste cigarette filter is an economic feasible approach for simultaneous solid wastes disposal. Herein, waste cigarette filter was used to prepare AFC through hot-pressing approach, which was convinced to have good adsorption efficiency on NH₃ due to large specific surface area. Effects of hot-pressing temperature, pressure and pressing time on AFC mechanical property and NH₃ adsorption efficiencies were optimized by response surface method. As results, hot-pressing treatment improved the specific surface area of AFC to 9.530 m²/g, and thus enhanced NH₃ adsorption efficiency to 68.73 % under hot-pressing temperature of 146 °C, pressure of 12.5 kPa and pressing time of 33 min. While the optimal tensile strength of AFC was obtained as 90.43 N under hot-pressing temperature of 140 °C, pressure of 15.0 kPa and pressing time of 30 min. The work provided an economic feasible approach for waste cigarette filter recycling and odor control.

Isotherm models for adsorption of heavy metals from water - A review

Adsorption is a widely used technology for removing and separating heavy metal from water, attributed to its eco-friendly, cost-effective, and high efficiency. Adsorption isotherm modeling has been used for many years to predict the adsorption equilibrium mechanism, adsorption capacity, and the inherent characteristics of the adsorption process, all of which are substantial in evaluating the performance of adsorbents. This review summarizes the development history, fundamental characteristics, and mathematical derivations of various isotherm models, along with their applicable conditions and application scenarios in heavy metal adsorption. The latest progress in applying isotherm models with a one-parameter, two-parameter, and three-parameter in heavy metal adsorption using carbon-based materials, which has gained much attention in recent years as low-cost adsorbents, is critically reviewed and discussed. Several experimental factors affecting the adsorption equilibrium, such as solution pH, temperature, ionic strength, adsorbent dose, and initial heavy metal concentration, are briefly discussed. The criteria for selecting the optimum isotherm for heavy metal adsorption are proposed by comparing various adsorption models and analyzing mathematical error functions. Finally, the relative performance of different isotherm models for heavy metal adsorption is compared, and the future research gaps are identified.

Review of Advanced Oxidation Processes Based on Peracetic Acid for Organic Pollutants

In recent years, the removal of organic pollutants from water and wastewater has attracted more attention to different advanced oxidation processes (AOPs). There has been increasing interest in using peroxyacetic acid (PAA), an emerging oxidant with low or no toxic by-products, yet the promotion and application are limited by unclear activation mechanisms and complex preparation processes. This paper synthesized the related research results reported on the removal of organic pollutants by PAA-based AOPs. Based on the research of others, this paper not only introduced the preparation method and characteristics of PAA but also summarized the mechanism and reactivity of PAA activated by the free radical pathway and discussed the main influencing factors. Furthermore, the principle and application of the newly discovered methods of non-radical activation of PAA in recent years were also reviewed for the first time. Finally, the shortcomings and development of PAA-based AOPs were discussed and prospected. This review provides a reference for the development of activated PAA technology that can be practically applied to the treatment of organic pollutants in water.

Recent Advancements in Cyclodextrin-Based Adsorbents for the Removal of Hazardous Pollutants from Waters

Water is an essential substance for the survival on Earth of all living organisms. However, population growth has disturbed the natural phenomenon of living, due to industrial growth to meet ever expanding demands, and, hence, an exponential increase in environmental pollution has been reported in the last few decades. Moreover, water pollution has drawn major attention for its adverse effects on human health and the ecosystem. Various techniques have been used to treat wastewater, including biofiltration, activated sludge, membrane filtration, active oxidation process and adsorption. Among the mentioned, the last method is becoming very popular. Moreover, among the sorbents, those based on cyclodextrin have gained worldwide attention due to their excellent properties. This review article overviewed recent contributions related to the synthesis of Cyclodextrin (CD)-based adsorbents to treat wastewater, and their applications, especially for the removal of heavy metals, dyes, and organic pollutants (pharmaceuticals and endocrine disruptor chemicals). Furthermore, new adsorption trends and trials related to CD-based materials are also discussed regarding their regenerative potential. Finally, this review could be an inspiration for new research and could also anticipate future directions and challenges associated with CD-based adsorbents.

Comparison of Organic Matter Properties and Disinfection By-Product Formation between the Typical Groundwater and Surface Water

The disinfection by-product (DBP) formation was affected by the dissolved organic matter (DOM). Therefore, the DOM properties and DBP formation potential of the two most widely used source waters: groundwater (GW) and surface water (SW), were comparatively studied in this work. The results suggested that the GW mainly consisted of protein-like organics with smaller molecular weight (Mw) less than 3000 Da, while the SW contained the humic- and fulvic-like substances with larger Mw. The tap water DBP concentration of GW as source water was lower than that of SW as well as the cytotoxic index (CI). The total DBP formation potential of the SW under chlorine and chloramine disinfection was higher than that of GW, especially the trihalomethanes (THMs) and haloacetic acid (HAAs). The higher THM and HAA formation potential of the SW was mainly attributed to the relatively hydrophobic and aromatic humic and fulvic substances. The halonitromethanes (HANs) formation was mainly due to the less hydrophobic protein-like components with smaller Mw. In addition, the total CI of the GW was lower than the SW under both chlorine and chloramine disinfection. Therefore, for the DBPs control, using the GW as source water was more beneficial to human health.