Effects of carbon nanotubes on phosphorus adsorption behaviors on aquatic sediments

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.

Investigation on the adsorption and desorption behaviors of heavy metals by tire wear particles with or without UV ageing processes

In recent years, tire wear particles (TWP), as the significant proportion of microplastics (MPs), has adsorbed much attention due to its widespread presence in aquatic ecosystem. Compared with typical MPs, TWP exists significant differences in composition, additives, characteristics and so on. With TWP and polypropylene (PP) as target MPs, Cd²⁺ and Pb²⁺ as target pollutants, the adsorption-desorption characteristics of heavy metal ions on original and aged MPs were studied. Compare with the PP, the S_BET of TWP increased more significantly after the UV ageing process. Meanwhile, the zeta potential of TWP increased from -8.01 to -14.6 mV and PP from -5.36 to -9.52 mV, and the surface of the TWP were more negatively-charged. In addition, the hydrophilicity of MPs enhanced due to the increased oxygen-containing functional groups after ageing process. Compared with PP, the physicochemical properties of TWP changed more obviously during UV ageing processes. The adsorption results showed that the pseudo-second-order model could better describe the adsorption processes of Cd²⁺ and Pb²⁺ on MPs. Meanwhile, the orders of adsorption capacity of MPs for Cd²⁺ and Pb²⁺ were aged TWP > aged PP > original TWP > original PP. The phenomenon of adsorption confirmed that TWP had better vector effects for heavy metal ions than PP, and the ageing processes could enhance the adsorption capacity of MPs. Moreover, the desorption results demonstrated that, compared with PP, the TWP (with higher adsorption capacity) also had the better desorption capacity for heavy metal ions in simulated gastric fluid. Compared with PP, the TWP might cause a more serious hazard to aquatic environment and organisms. These investigations would contribute to assessing the potential environmental and biological risk of TWP, especially considering the effect of the ageing process.

Investigation on the adsorption of antibiotics from water by metal loaded sewage sludge biochar

Application of sewage sludge biochar as an adsorbent for antibiotics treatment has obtained special attention owning to its low cost and surface functionality. Three metal ions were selected to modify sewage sludge biochar through the pyrolysis with the metal loaded method. Fe loaded sewage sludge biochar (BC-Fe), Al loaded sewage sludge biochar (BC-Al) and Mn loaded sewage sludge biochar (BC-Mn) were characterized and used to explore the performance of adsorbing tetracycline (TC), sulfamethoxazole (SMZ) and amoxicillin (AMC). BC-Fe, BC-Al and BC-Mn possessed rougher surfaces, larger specific surface area and better pore structure. Intra-particle diffusion and Langmuir models were more suitable to describe the adsorption process. The maximum adsorption amount of TC, SMZ and AMC could reach 123.35, 99.01 and 109.89 mg/g by BC-Fe. Furthermore, the main mechanism of antibiotics adsorption by metal loaded sewage sludge biochars might be pores filling, Van der Waals forces and H-bonding. The study can not only solve the problems associated with the pollution of antibiotics from wastewater, but also reduced the treatment pressure of sewage sludge effectively.

Interaction between multi-walled carbon nanotubes and propranolol

Carbon nanotubes could accumulate in organism and have a negative impact on the structure and function of the ecosystem when they were discharged into environment. Furthermore, it will affect the migration and fate of pollutants in the water body. The study is mainly to explore the adsorption behavior and mechanism of beta-blocker on multi-walled carbon nanotubes (MWCNTs). Propranolol (PRO) was selected as the representative of beta-blocker. The effects of different environmental factors such as pH, ionic strength and humic acid (HA) on the adsorption process were investigated. The adsorption results were characterized by Zeta potential. At the same time, the effects of different types of drugs on the adsorption process were explored and the possible adsorption mechanisms were analyzed. The experimental results showed that the adsorption behavior was significantly different under different pH conditions. π-π EDA interaction, hydrophobic interaction and hydrogen bonding were speculated to be the main adsorption mechanisms for PRO adsorption on MWCNTs.

Utilization of nanomaterials for in-situ remediation of heavy metal(loid) contaminated sediments: A review

Heavy metal(loid)s are toxic and non-biodegradable environmental pollutants. The contamination of sediments with heavy metal(loid)s has attracted increasing attention due to the negative environmental effects of heavy metal(loid)s and the development of new remediation techniques for metal(loid) contaminated sediments. As a result of rapid nanotechnology development, nanomaterials are also being increasingly utilized for the remediation of contaminated sediments due to their excellent capacity of immobilizing/adsorbing metal(loid) ions. This review summarizes recent studies that have used various nanomaterials such as nanoscale zero-valent iron (nZVI), stabilizer-modified nZVI, nano apatite based-materials including nano-hydroxyapatite particles (nHAp) and stabilized nano-chlorapatite (nCLAP), carbon nanotubes (CNTs), and titanium dioxide nanoparticles (TiO₂ NPs) for the remediation of heavy metal(loid) contaminated sediments. We also review the analysis of potential mechanisms involved in the interaction of nanomaterials with metal(loid) ions. Subsequently, we discuss the factors affecting the nanoparticle-heavy metal(loid)s interaction, the environmental impacts resulting from the application of nanomaterials, the knowledge gaps, and potential future research.

Unraveling adsorption behavior and mechanism of perfluorooctane sulfonate (PFOS) on aging aquatic sediments contaminated with engineered nano-TiO2

Engineered nano-TiO₂ (Enano-TiO₂) have inevitably discharged into aquatic sediments that resulted from their widespread use. The physicochemical characteristics of sediments might be changed because of remarkable properties of Enano-TiO₂ and affected by the aging of sediments, thereby altering the environmental behavior and bioavailability of other pollutants such as perfluorooctane sulfonate (PFOS) in sediments. Here, adsorption behavior and mechanism of PFOS on aging aquatic sediments spiked with Enano-TiO₂ at a weight ratio of 5.0% were investigated. The results showed that Enano-TiO₂ significantly altered zero points of charge (pH_zpc) and pore surface properties of sediments, manifested as pH_zpc, the total surface area (S_BET), the micro-pore surface area (S_micro), and the external surface area (S_ext) of sediment particles contaminated with Enano-TiO₂ clearly increased, instead average pore size decreased. Rapid intra-particle diffusion processes were well fitted by the pseudo-second-order rate model with the sorption rate (K₂) following the order single (5.764 mg/(g·h)) > binary systems (3.393 mg/(g·h)). Freundlich model best described the sorption isotherm data with the larger sorption capacity (K_F) and sorption affinity (1/n) of sediments spiked with Enano-TiO₂ than that of sediments only. Additionally, Enano-TiO₂ changed the adsorption thermodynamics of PFOS on the sediments with the absolute value of ∆G⁰, ∆H⁰, and ∆S⁰ increased. Fourier transform infrared (FT-IR) spectroscopy suggested possible formation of a negative charge-assisted H-bond between PFOS and the functionalities on sediment surfaces, including O-H of carboxyl, alcohol, phenols, and chemisorbed H₂O as well as carbonyl groups (C=O) of ketone groups. Furthermore, the multilayer sorption of PFOS on sediments contaminated with Enano-TiO₂ is plausible because of bridging effect of Cu²⁺ and Pb²⁺.