One-step synthesis of a β-cyclodextrin derivative and its performance for the removal of Pb(II) from aqueous solutions

Selective and Accurate Detection of Nitrate in Aquaculture Water with Surface-Enhanced Raman Scattering (SERS) Using Gold Nanoparticles Decorated with β-Cyclodextrins

A surface-enhanced Raman scattering (SERS) method for measuring nitrate nitrogen in aquaculture water was developed using a substrate of β-cyclodextrin-modified gold nanoparticles (SH-β-CD@AuNPs). Addressing the issues of low sensitivity, narrow linear range, and relatively poor selectivity of single metal nanoparticles in the SERS detection of nitrate nitrogen, we combined metal nanoparticles with cyclodextrin supramolecular compounds to prepare a AuNPs substrate enveloped by cyclodextrin, which exhibits ultra-high selectivity and Raman activity. Subsequently, vanadium(III) chloride was used to convert nitrate ions into nitrite ions. The adsorption mechanism between the reaction product benzotriazole (BTAH) of o-phenylenediamine (OPD) and nitrite ions on the SH-β-CD@AuNPs substrate was studied through SERS, achieving the simultaneous detection of nitrate nitrogen and nitrite nitrogen. The experimental results show that BTAH exhibits distinct SERS characteristic peaks at 1168, 1240, 1375, and 1600 cm-1, with the lowest detection limits of 3.33 × 10-2, 5.84 × 10-2, 2.40 × 10-2, and 1.05 × 10-2 μmol/L, respectively, and a linear range of 0.1-30.0 μmol/L. The proposed method provides an effective tool for the selective and accurate online detection of nitrite and nitrate nitrogen in aquaculture water.

Multi-component adsorption of Pb(II), Cd(II) and Ni(II) onto microwave-functionalized cellulose: Kinetics, isotherms, thermodynamics, mechanisms and application for electroplating wastewater purification

Herein, microwave-functionalized cellulose derived from rice husk was cost-effectively prepared and employed for Pb(II), Cd(II) and Ni(II) elimination in mono- and multi-component systems. Benefiting from microwave irradiation, the functionalized process was achieved in 6.5 min and the resultant RH_MW-X possessed remarkably high adsorption capacities of 295.20 mg/g for Pb(II), 151.51 mg/g for Cd(II) and 72.80 mg/g for Ni(II) within the equilibrium time of 30 min. Noticeably, the metal ions adsorption rate and capacity in binary and ternary systems were lower than that of unary systems. The coexistence of Cd(II) and Ni(II) significantly slowed down the Pb(II) adsorption in binary and ternary systems, while Pb(II) exhibited the most obvious influence on the metal ions uptake in the multi-component systems. FT-IR and XPS results revealed that both ion exchange and chelation were functioned in the metal ions uptake, while physical interaction was also involved in the adsorption process. Moreover, the RH_MW-X possessed favorable recyclability with slight adsorption efficiency decline during five cycles in different systems. Particularly, the RH_MW-X could effectively purify actual industrial wastewater containing Pb(II), Cd(II) and Ni(II) for meeting regulatory requirements. This work facilitates the omnidirectional improvement of adsorbents for the de-pollution of practical heavy metals wastewater.

Supramolecular adsorption of cyclodextrin/polyvinyl alcohol film for purification of organic wastewater

Into purified organic wastewater, α-, β-, and γ-cyclodextrin (α-, β-, and γ-CD) were added to polyvinyl alcohol (PVA) with ammonium persulfate as the crosslinker. The CD/PVA composite film with low water solubility and supramolecular adsorption was prepared by solvent evaporation. Fourier transform infrared spectroscopy showed that when CD was successfully added to PVA, the crosslinking process had no effect on -OH, and the structure was stable after soaking in water for 120 h. Solubility experiments showed that the stability of PVA in water was significantly improved. The results of phenolphthalein adsorption showed that the composite film followed the Langmuir isothermal adsorption and the pseudo-second-order kinetics. According to the Langmuir equation, the theoretical maximum adsorption capacities of α-, β- and γ-CD/PVA composite films were 0.41, 2.05, and 2.00 mg/g, respectively. The parameters of the Freundlich equation indicate that the adsorption of the composite film is physical adsorption. The time for α-CD/PVA composite film to reach equilibrium was the shortest, while the longest was for β-CD/PVA composite film. The intraparticle diffusion model showed that the adsorption was mainly affected by the diffusion of the boundary layer, and the diffusion rate limitation of the boundary layer of the high-concentration phenolphthalein solution was more obvious.

A combined system of microwave-functionalized rice husk and poly-aluminium chloride for trace cadmium-contaminated source water purification: Exploration of removal efficiency and mechanism

Cadmium is highly poisonous to mammals and related water pollution incidents are increasing world-widely. Here, the clean-up of trace Cd(II) by a combined process of microwave-functionalized rice husk (RH_MW-M) and poly aluminium chloride (PAC) was investigated for the first time, with the exploration of removal mechanism and efficacy. Microwave irradiation was found to be a new approach to achieve the functionalized procedure, which could decrease the processing time from 2.5 h to 390 s with the Cd(II) uptake of the outcome product soaring from 137.16 mg/g to 191.32 mg/g. The ultra-rapidly prepared RH_MW-M exhibited a fast adsorption equilibrium within 30 min over a wide pH range of 5.0-8.0, and the FT-IR and XPS studies confirmed that both ion exchange and chelation were functioned in the Cd(II) uptake process. Controlled by the turbidity threshold of drinking water treatment plant, the feasible dosage of RH_MW-M in the absence and presence of 30 mg/L PAC increased from 30 to 760 mg/L, which could effectively deal with the trace Cd(II) at the concentration from 33 μg/L up to 0.933 mg/L, exhibiting much better performance than traditional alkali precipitation. Predictably, this simple and scalable RH_MW-M/PAC system could afford a promising end-of-pipe solution for heavy-metal contamination.

Adsorption performance and mechanisms of Pb(II), Cd(II), and Mn(II) removal by a β-cyclodextrin derivative

In this study, the novel adsorbent PVA-TA-βCD was synthesized via thermal cross-linking between polyvinyl alcohol and β-cyclodextrin. The characterization methods SEM-EDS, FTIR, and XPS were adopted to characterize the adsorbent. The effect of pH, contact time, initial concentrations, and temperature during the adsorption of Pb(II), Cd(II), and Mn(II) onto the PVA-TA-βCD was also investigated. In a single-component system, the data fitted well to pseudo-second-order, and film diffusion and intra-particle diffusion both played important roles in the adsorption process. As for isotherm study, it showed a heterogeneous adsorption capacity of 199.11, 116.52, and 90.28 mg g^-1 for the Pb(II), Cd(II), and Mn(II), respectively. Competition between the ions existed in a multi-component system; however, owing to the stronger affinity of the PVA-TA-βCD for Pb(II) relative to Cd(II) and Mn(II), the Pb(II) adsorption onto the PVA-TA-βCD was less affected by the addition of the other metals, which could be effectively explained by the hard and soft acid and base theory (HSAB). Furthermore, PVA-TA-βCD showed good reusability throughout regeneration experiments.