Surface modification of Carbon-Based Nanoadsorbents for the Advanced Wastewater Treatment

Utilizing sludge-based activated carbon for targeted leachate mitigation in wastewater treatment

Activated carbon (AC) based adsorbents derived from waste sludge were utilized to remediate mixed contaminants in wastewater as an integrated waste-to-resource approach promoting a paradigm shift in management of refuse sludge and wastewater. This review specifically focuses on the remediation of constituents of landfill leachate by sludge-based activated carbon (SBAC). The adsorption effectiveness of SBAC for the exclusion of leachate characters including heavy metals, phenols, dyes, phosphates, and phosphorus were explored with regard to modifiers such as pH, temperature, properties of the adsorbent including functional groups, initial doses of absorbent and adsorbate, and duration of exposure to note the impact of each parameter on the efficiency of adsorption of the sludge adsorbent. Through the works of various researchers, it was noted that the properties of the adsorbent, pH and temperature impact the working of SBACs. The pH of the adsorbent by influencing the functional groups. Temperature was expected to have a paramount effect on the adsorption efficiency of the SBACs. The importance of the regeneration and recycling of the adsorbents as well as their leachability is highlighted. Sludge based activated carbon is recommended as a timely, resource-efficient, and sustainable approach for the remediation of wastewater.

Sustainable adsorbent frameworks based on bio-resourced materials and biodegradable polymers in selective phosphate removal for waste-water remediation

Phosphorus to an optimum extent is an essential nutrient for all living organisms and its scarcity may cause food security, and environmental preservation issues vis-à-vis agroeconomic hurdles. Undesirably excess phosphorus intensifies the eutrophication problem in non-marine water bodies and disrupts the natural nutrient balance of the ecosystem. To overcome such dichotomy, biodegradable polymer-based adsorbents have emerged as a cost-effective and implementable approach in striking a "desired optimum-undesired excess" balance pertaining to phosphate in a sustainable manner. So far, the reports on adopting such adsorbent-approach for wastewater remediation remained largely scattered, unstructured, and poorly correlated. In this background, the contextual review comprehensively discusses the current state-of-the-art in utilizing biodegradable polymeric frameworks as an adsorbent system for phosphate removal and its efficient recovery from the aquatic ecosystem, while highlighting their characteristics-specific functional efficiency vis-à-vis easiness of synthetic and commercial viability. The overview further delves into the sources and environmental ramifications of excessive phosphorus in water bodies and associated mechanistic pathways of phosphorus removal via adsorption, precipitation, and membrane filtration enabled by biodegradable (natural and synthetic) polymeric substrates. Finally, functionality optimization, degradability tuning, and adsorption selectivity of biodegradable polymers are highlighted, while aiming to strike a balance in "removal-recovery-reuse" dynamics of phosphate. Thus, the current review not only paves the way for future exploration of biodegradable polymers in sustainable cost-effective adsorbents for phosphorus removal but also can serve as a guide for researchers dealing with this critical issue.

Applications and implications of carbon nanotubes for the sequestration of organic and inorganic pollutants from wastewater

The rapid growth in the population, industrial developments, and climate change over the century have contributed to a significant rise in aquatic pollution leading to a scarcity of clean, reliable, and sustainable water sources and supply. Exposure through ingestion, inhalation, and dermal absorption of organic/inorganic compounds such as heavy metals, pharmaceuticals, dyes, and persistent organic pollutants (POPs) discharged from municipalities, hospitals, textile industries, food, and agricultural sectors has caused adverse health outcomes in aquatic and terrestrial organisms. Owing to the high surface area, photocatalytic activity, antimicrobial, antifouling, optical, electronic, and magnetic properties, the application of nanotechnology offers unique opportunities in advanced wastewater management strategies over traditional approaches. Carbon nanomaterials and associated composites such as single-walled carbon nanotubes (SWCNT), multiwalled carbon nanotubes (MWCNT), and carbon nanotubes (CNT) buckypaper membranes have demonstrated efficiency in adsorption, photocatalytic activity, and filtration of contaminants and thus show immense potentiality in wastewater management. This review focuses on the application of CNTs in the sequestration of organic and inorganic contaminants from the aquatic environment. It also sheds light on the aquatic pollutant desorption processes, current safety regulations, and toxic responses associated with CNTs. Critical knowledge gaps involving CNT synthesis, surface modification processes, CNT-environment interactions, and risk assessments are further identified and discussed.

Treatment of Multi-Walled Carbon Nanotubes with Dichromic Acid: Oxidation and Appearance of Intercalation

This work is dedicated to the study of the treatment of multi-walled carbon nanotubes (MWCNTs) with dichromic acid. The dichromic acid was formed by dissolving different concentrations of CrO3 in water. The effect of the concentration of dichromic acid on the change in texture characteristics, elemental composition, defectiveness, graphitization degree, and surface chemistry of MWCNTs was investigated using various analytical techniques, such as transmission electron microscopy, energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). Testing of MWCNTs as electrodes for supercapacitors in 3.5 M H2SO4 solution was carried out using cyclic voltammetry. A decrease in the average diameter of CNTs after treatment was found. The EDX and XPS showed that the oxygen content on the surface of MWCNTs increased after treatment with dichromic acid. The formation of Cr2O3 after treatment with dichromic acid was detected by XPS. High angle annular dark field scanning transmission electron microscopy was used to confirm the intercalation of the chromium-containing compound between graphene layers of MWCNTs after treatment with dichromic acid. It was found that two different types of MWCNTs showed diverse behavior after treatment. The highest specific capacitance of the MWCNTs after treatment was 141 F g-1 (at 2 mV s-1) compared to 0.3 F g-1 for the untreated sample.

Green composites based on volcanic red algae Cyanidiales, cellulose, and coffee waste biomass modified with magnetic nanoparticles for the removal of methylene blue

In this paper, green nanocomposites based on biomass and superparamagnetic nanoparticles were synthesized and used as adsorbents to remove methylene blue (MB) from water with magnetic separation. The adsorbents were synthesized through the wet co-precipitation technique, in which iron-oxide nanoparticles coated the cores based on coffee, cellulose, and red volcanic algae waste. The procedure resulted in materials that could be easily separated from aqueous solutions with magnets. The morphology and chemical composition of the nanocomposites were characterized by SEM, FT-IR, and XPS methods. The adsorption studies of MB removal with UV-vis spectrometry showed that the adsorption performance of the prepared materials strongly depended on their morphology and the type of the organic adsorbent. The adsorption studies presented the highest effectiveness in neutral pH with only a slight effect on ionic strength. The MB removal undergoes pseudo-second kinetics for all adsorbents. The maximal adsorption capacity for the coffee@Fe₃O₄-2, cellulose@Fe₃O₄-1, and algae@Fe₃O₄-1 is 38.23 mg g^-1, 41.61 mg g^-1, and 48.41 mg g^-1, respectively. The mechanism of MB adsorption follows the Langmuir model using coffee@Fe₃O₄ and cellulose@Fe₃O₄, while for algae@Fe₃O₄ the process fits to the Redlich-Peterson model. The removal efficiency analysis based on UV-vis adsorption spectra revealed that the adsorption effectiveness of the nanocomposites increased as follows: coffee@Fe₃O₄-2 > cellulose@Fe₃O₄-1 > algae@Fe₃O₄-1, demonstrating an MB removal efficiency of up to 90%.

Super-adsorbent microspheres based on a triallyl isocyanurate-maleic anhydride copolymer for the removal of organic pollutants from water

Owing to the frequent occurrence of diclofenac sodium (DS) in fresh aquatic environments and its potential toxicity towards living organisms, the effective removal of DS has attracted worldwide attention. Herein, a green and efficient strategy to fabricate crosslinked microspheres with interconnected mesoporous structures and abundant adsorption active sites was developed. With this strategy, triallyl isocyanurate (TAIC)-maleic anhydride (MAH) copolymer microspheres (TMs) with a diameter of 1.19-1.35 μm were first prepared by self-stabilized precipitation (2SP) polymerization, and the TMs possess a large amount reactive anhydride groups (62.5-71.8 mol%), a specific surface area of 51.6-182.4 m² g^-1 and a mesoporous structure (average pore size: 3.4-3.8 nm). Then the TMs were further functionalized with polyethylenimine (PEI) to give rise to cationic microspheres (Cat-TMs), which showed excellent adsorption performance to DS with a rapid adsorption rate (reached equilibrium within 30 min), a very high equilibrium adsorption capacity (1421 mg g^-1) and excellent recyclability. The pseudo-second-order model and Langmuir model were a good fit for the adsorption kinetic and isotherm process, respectively. Furthermore, due to the high cation density (4.291 mmol g^-1) and excellent pH buffer capacity of Cat-TMs, the adsorption capacity can be maintained at a high level within the pH range of 6-10. The regenerated Cat-TMs showed only a slight loss (<5%) in the adsorption capacity even after 5 adsorption-desorption cycles. In short, Cat-TMs can be considered as a highly promising adsorbent for the rapid and ultra-efficient removal of anionic organic contaminants and have significant potential to be applied in wastewater treatment.

Purification and water resource circulation utilization of Cd-containing wastewater during microbial remediation of Cd-polluted soil

The purification and water resource circulation utilization of cadmium-containing leachate is a key link in the field application of microbial remediation in Cd-polluted soil. In this study, through a simulation experiment of microbial remediation of Cd-polluted paddy soil, the feasibility of the purification and recycling process of wastewater derived from microbial remediation of Cd-polluted soil was explored. The results of the microbial mobilization and removal experiment showed that the concentrations of Cd, N, P, and K in the leachate were 88.51 μg/L, 38.06, 0.53, and 98.87 mg/L, respectively. The leachate also contained a large number of microbial resources, indicating that it had high recovery values. To recycle this wastewater, activated carbon (C), humic acid (H), and self-assembled monolayers on mesoporous supports (SAMMS; S) were used as adsorbents. The results showed that the co-existing cations in the leachate had a major influence on the adsorption of Cd. In the ternary system of Fe, Al, and Cd, the removal efficiency of Cd increased to 91.2% when the S dosage was increased to 5‰, and the sorption of Cd occurred after Fe and Al. However, C and H exhibited poor adsorption performances. The isotherm models further showed that the maximum adsorption capacities of S, H, and C were 13.96, 6.41 and 2.94 mg/g, respectively. The adsorption kinetics of S showed that adsorption was a rapid process, and the C-H and O-Si-O of S were the key functional groups. The pH of the leachate significantly affected the adsorption efficiency of Cd. Finally, the purified leachate was successfully applied to microbial cultivation and soil remediation. Overall, the reclamation of Cd-containing wastewater can not only dampen the impacts of water shortages, but also achieve the purposes of Cd removal and resource recovery to lower costs by approximately 1166-3499 yuan per mu.

Preconcentration and Removal of Pb(II) Ions from Aqueous Solutions Using Graphene-Based Nanomaterials

Direct determination of lead trace concentration in the presence of relatively complex matrices is often a problem. Thus, its preconcentration and separation are necessary in the analytical procedures. Graphene-based nanomaterials have attracted significant interest as potential adsorbents for Pb(II) preconcentration and removal due to their high specific surface area, exceptional porosities, numerous adsorption sites and functionalization ease. Particularly, incorporation of magnetic particles with graphene adsorbents offers an effective approach to overcome the separation problems after a lead enrichment step. This paper summarizes the developments in the applications of graphene-based adsorbents in conventional solid-phase extraction column packing and its alternative approaches in the past 5 years.

Wastewater treatment with nanomaterials for the future: A state-of-the-art review

Aquatic and terrestrial ecosystems are both threatened by toxic wastewater. The unique properties of nanomaterials are currently being studied thoroughly for treating sewage. Nanomaterials also have the advantage of being capable of removing organic matter, fungi, and viruses from wastewater. Advanced oxidation processes are used in nanomaterials to treat wastewater. Additionally, nanomaterials have a large effective area of contact due to their tiny dimensions. The adsorption and reactivity of nanomaterials are strong. Wastewater treatment would benefit from the development of nanomaterial technology. Second, the paper provides a comprehensive analysis of the unique characteristics of nanomaterials in wastewater treatment, their proper use, and their prospects. In addition to focusing on their economic feasibility, since limited forms of nanomaterials have been manufactured, it is also necessary to consider their feasibility in terms of their technical results. According to this study, the significant adsorption area, excellent chemical reaction, and electrical conductivity of nanoparticles (NPs) contribute to the successful treatment of wastewater.

Functionalization of graphene nanostructures with inorganic nanoparticles and their use for the removal of pharmaceutical pollutants in water

Emerging pollutants such as pharmaceuticals are of special concern because despite their low environmental concentration, their biological activity can be intense, and they should be prevented to reach uncontrolledly to the environment. A graphene-based hybrid material decorated with Fe3O4 and TiO2 nanoparticles (NPs) has been prepared to effectively remove emerging pollutants as nonsteroidal anti-inflammatory drugs (NSAIDs) Ibuprofen and Diclofenac present in water at low environmental concentrations by a one-step functionalization process following a novel gentle and scalable surfactant depletion approach. Following this methodology, nanoparticles are progressively deprived of their original surfactant in the presence of graphene, leading to the formation of hybrid nanostructures composed of two different types of nanoparticles well dispersed over the graphene nanosheets. Ibuprofen and Diclofenac adsorption kinetics on the composites was investigated via UV-Vis spectroscopy. The as prepared hybrid material possesses high adsorption capacity, superparamagnetic properties, photocatalytic behavior, and good water dispersibility. Thanks to incorporating TiO2 nanoparticles as in situ catalysts, the adsorption performance of composites is restored after use, which could be a promising recycling pathway for the adsorbents in wastewater treatments.

Removal of Pb2+, CrT, and Hg2+ Ions from Aqueous Solutions Using Amino-Functionalized Magnetic Nanoparticles

In this paper, a circular economy approach with the adsorption and desorption of heavy metal (HM) ions—i.e., lead (Pb2+), chromium (CrT), and mercury (Hg2+)—from aqueous solutions was studied. Specific and selective binding of HM ions was performed on stabilized and amino-functionalized iron oxide magnetic nanoparticles (γ-Fe2O3@NH2 NPs) from an aqueous solution at pH 4 and 7. For this purpose, γ-Fe2O3@NH2 NPs were characterized by thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), specific surface area (BET), transmission electron microscopy (TEM), EDXS, and zeta potential measurements (ζ). The effects of different adsorbent amounts (mads = 20/45/90 mg) and the type of anions (NO3−, Cl−, SO42−) on adsorption efficiency were also tested. The desorption was performed with 0.1 M HNO3. The results showed improvement of adsorption efficiency for CrT, Pb2+, and Hg2+ ions at pH 7 by 45 mg of g-Fe2O3@NH2 NPs, and the sequence was as follows: CrT > Hg2+ > Pb2+, with adsorption capacities of 90.4 mg/g, 85.6 mg/g, and 83.6 mg/g, respectively. The desorption results showed the possibility for the reuse of γ-Fe2O3@NH2 NPs with HNO3, as the desorption efficiency was 100% for Hg2+ ions, 96.7% for CrT, and 91.3% for Pb2+.

Emerging Trends in the Remediation of Persistent Organic Pollutants Using Nanomaterials and Related Processes: A Review

Persistent organic pollutants (POPs) have become a major global concern due to their large amount of utilization every year and their calcitrant nature. Due to their continuous utilization and calcitrant nature, it has led to several environmental hazards. The conventional approaches are expensive, less efficient, laborious, time-consuming, and expensive. Therefore, here in this review the authors suggest the shortcomings of conventional techniques by using nanoparticles and nanotechnology. Nanotechnology has shown immense potential for the remediation of such POPs within a short period of time with high efficiency. The present review highlights the use of nanoremediation technologies for the removal of POPs with a special focus on nanocatalysis, nanofiltration, and nanoadsorption processes. Nanoparticles such as clays, zinc oxide, iron oxide, aluminum oxide, and their composites have been used widely for the efficient remediation of POPs. Moreover, filtrations such as nanofiltration and ultrafiltration have also shown interest in the remediation of POPs from wastewater. From several pieces of literature, it has been found that nano-based techniques have shown complete removal of POPs from wastewater in comparison to conventional methods, but the cost is one of the major issues when it comes to nano- and ultrafiltration. Future research in nano-based techniques for POP remediation will solve the cost issue and will make it one of the most widely accepted and available techniques. Nano-based processes provide a sustainable solution to the problem of POPs.

Why reuse spent adsorbents? The latest challenges and limitations

Despite the abundance of published reviews over the last few years, the inconsistent data representation in regards to the use of adsorbents in each work, renders the task of comparing them challenging. Disposing the adsorbent may have adverse environmental impact, which should be mitigated through regeneration and reuse processes, such as desorption. This review discusses how the importance of desorption and regeneration equates that of the adsorption stage, and presents various regeneration methods as well as the influencing parameters, advantages, and disadvantages thereof. For the purposes of this work, the adsorbents have been categorized into four groups: (i) graphene, (ii) carbon nanotubes, (iii) activated carbon compounds and (iv) clays and polymer adsorbents as representatives in order to further study their desorption and regeneration abilities, using a variety of desorption media/eluants. The process conditions, such as pH, dose required, concentration, adsorption ability and the cost of the adsorbents were examined for further analysis. The recovery efficiency and ability to get reused through the desorption process was also evaluated. The highest adsorption capacity was observed for graphene-based adsorbents reaching between 108 and >480 mg/g, and for activated carbon materials ranging from 34 to >384 mg/g, whereas carbon nanotubes and polymer-based adsorbents indicated rather low and greatly varying adsorption capacities, between 1 and >138 mg/g and between 7 and >57 mg/g, respectively. Most of the reviewed cases appear to fit the pseudo-second order (PSO) kinetic model. These materials have demonstrated a removal effectiveness between 71% and 99%. Overall, all the aforementioned adsorbents share the advantage of being highly reusable.

Adsorption of Rare Earth Ce3+ and Pr3+ Ions by Hydrophobic Ionic Liquid

This study reports the use of hydrophobic ionic liquid (IL) based on D-galactose for the recovery of Ce (III) and Pr (III) ions from solutions. The equilibrium data were obtained by optimization of batch parameters, and various isotherms and kinetic models were utilised to predict the mechanistic process of sequestration of ions. The Arrhenius activation energies are found to be between 5-40 kJ, suggesting the physisorption process of ions onto IL. The present process is understood to be rapid and exothermic in nature according to thermodynamic experiments. The loading capacity was found to be 179.3 g L-1 and 141.5 g L-1, respectively, for Ce (III) and Pr (III) ions at pH 5 with a contact time of 30 min and dose being 0.1 g L-1. The higher uptake capacity is attributed to the presence of a highly electronegative fluorine atom in the IL. These results highlight the potential application of IL in the sequestration of Ce (III) and Pr (III) ions from any water sources.