The study aims to use waste plastic PET bottles to recover terephthalic acid for preparing copper-1,4-benzenedicarboxylate, which was then utilized as an adsorbent for removal of methylene blue (MB) from aqueous solutions after carefully characterizing by XRD, FTIR, TGA, SEM, and EDX. The optimum conditions were established as pH = 6, 25°C, adsorbent dose of 1 g L⁻¹, contact time of 20 min, and agitation speed of 150 rpm. The adsorption process was spontaneous, exothermic, fitting well to Langmuir isotherm model with the maximum adsorption capacity of 41.01 mg g⁻¹ and more suitable to be described by the pseudo first-order kinetic model. It was indicated that the physical adsorption plays a leading role in the adsorption process. The recycling study was also conducted to confirm the long-term use of the synthesized adsorbent.

Magnetic activated carbon/chitosan composite (MACCS) beads from spent coffee grounds and shrimp shells were synthesized using green tea extract as a crosslinker. The adsorbent was then applied for removal of Ni(II) ions from aqueous solution after carefully characterizing it by various techniques (XRD, FTIR, FE-SEM, EDX, VSM and BET). The adsorption kinetics, isotherms, thermodynamics, the effects of key adsorption factors such as the pH value, initial Ni(II) concentration, contact time, adsorbent dose and temperature were investigated in detail. A possible adsorption mechanism was proposed. The results indicated that the adsorption process was thermodynamically favourable, spontaneous, endothermic, and was best described by the Langmuir isotherm and pseudo-second-order kinetic models. The MACCS beads with an optimum CS to MAC weight ratio estimated as 60:40 gave the maximum monolayer adsorption capacity for Ni(II) ions of 108.70 mg g⁻¹ at 25°C, pH of 6, adsorbent dose of 1.0g L⁻¹ and a contact time of 6 h. The recycling study confirmed that the adsorption ability of MACCS beads towards Ni(II) ions maintained well after five consecutive cycles with the removal efficiency greater than 86.25%. Eventually, the MACCS beads could be used as an environmentally-friendly and highly efficient adsorbent for removal of Ni(II) ions from wastewater due to the advantages of high efficiency, rapid separation and good reusability. GRAPHICAL ABSTRACT

In the present work, a novel composite consisting of magnetite, activated carbon from spent coffee grounds and natural clay (MACCC) was prepared by a one-pot synthesis method via a simultaneous activation and magnetization processes. Various techniques (XRD, FTIR, SEM, TEM, EDX, BET) were utilized to characterize the synthesized composite before utilizing it as an adsorbent for removal of Cu(II), Ni(II) and Pb(II) ions from aqueous solutions. Conditions for removal of heavy metals were thoroughly optimized as 25 °C, pH of 5.5, adsorbent dosage of 2 g L⁻¹, and a contact time of 60 min. Three models of pseudo first-, second-order and intraparticle diffusion as well as three models of Langmuir, Freundlich, and Temkin were used to analyze kinetics and isotherms of the adsorption process. Thermodynamics was discussed completely. Regeneration and recyclability of the adsorbent were also evaluated. Based on the analysis of experimental results, a possible adsorption mechanism of heavy metals onto the synthesized composite was proposed. The maximum capacities caculated from Langmuir model followed the order of Pb(II) > Cu(II) > Ni(II) as 143.56, 96.16 and 84.86 mg·g⁻¹, respectively. The overall results indicated that MACCC is a potential adsorbent for removal of toxic Pb(II), Cu(II) and Ni(II) ions from wastewater due to simple preparation, high removal efficiency and good recyclability.

C/Ce-codoped ZnO nanoparticles immobilized onto multi-walled carbon nanotubes (C/Ce-ZnO@MWCNT) were successfully fabricated via the hydrothermal method for degradation of methylene blue (MB) under visible light irradiation. The prepared C/Ce-ZnO@MWCNT samples were characterized by XRD, XPS, FTIR, FE-SEM, EDX, BET, and diffuse reflectance spectroscopy. The obtained results indicated that the photocatalytic activity of all the MWCNTs-containing samples was higher than those of the bare ZnO and C/Ce-codoped ZnO nanoparticles. Besides, the C/Ce-ZnO@MWCNT composite with 50 wt% MWCNT showed the highest photocatalytic activity with the MB removal efficiency of 96.5% recorded within 90 min under visible light illumination using 1.0 g/L catalyst dosage at pH of 9 and MB concentration of 30 ppm. The degradation mechanism controlled by the charge transfer process in C/Ce-ZnO@MWCNT composite was proposed and discussed in detail. In addition, the long-term-use ability of the photocatalyst was also evaluated through experiments conducted in continuous cycles.