Adsorption of naphthalene polycyclic aromatic hydrocarbon from wastewater by a green magnetic composite based on chitosan and graphene oxide

A green magnetic composite mCS/GO was synthesized using water hyacinth extract, as a reducing agent, and proanthocyanidin, as a crosslinking agent, for the adsorption of naphthalene from effluents. The green composite was evaluated using different characterization techniques to determine its thermal (TG/DTG), structural (BET, XPS and FTIR), crystallographic (XRD), and textural (SEM) properties in natura and post-adsorption. The results obtained through a central composite design (CCD) experiment indicated that the initial concentration of NAP and the adsorbent dosage are significant for the adsorption capacity. The adsorption assays indicated that physisorption, through π-π and hydrophobic interactions, were the main mechanism involved in the NAP adsorption. However, the adjustment to the PSO and Freundlich models, obtained through kinetic and equilibrium studies, indicated that chemisorption also influences the adsorptive process. The thermodynamic study indicated physisorption as the mechanism responsible for the NAP adsorption. Also, the adsorbent has high affinity for the adsorbate and the process is spontaneous and endothermic. The maximum adsorption capacity (q_max) of the green mCS/GO was 334.37 mg g^-1 at 20 °C. Furthermore, the green mCS/GO was effectively regenerated with methanol and reused for five consecutive cycles, the percentage of NAP recovery went from approximately 91 to 75% after the fifth cycle. The green composite was also applied in the adsorption of NAP from river water samples, aiming to evaluate the feasibility of the method in real applications. The adsorption efficiency was approximately 70%. From what we know, this it is the first time that a green adsorbent was recycled after the polycyclic aromatic hydrocarbon (PAHs) adsorption process.

Effect of Ca2+ ions on naphthalene adsorption/desorption onto calcium oxide nanoparticle: Adsorption isotherm, kinetics and regeneration studies

The adsorptive nature of calcium oxide nanoparticles in aqueous sample of naphthalene in presence of Ca²⁺ ions was estimated. Enhanced efficiency of calcium oxide regeneration (90%) with the aid of calcium chloride in the solution concentration of 0.002-0.1 M was depicted. The less degree of toxic naphthalene desorption merged with SEM, FTIR and XRD characterization data portrays the importance of naphthalene adsorption onto calcium oxide using calcium chloride for regeneration. Batch adsorption studies were performed to evaluate the operating parameters such as pH, naphthalene concentration, contact time and impact of Ca²⁺ on naphthalene study. The adsorption isotherm of naphthalene on calcium oxide nanoparticle was described by Langmuir, Freundlich, Temkin and Dubinin Radushkevich and theoretical maximum monolayer adsorption capacity was found to be 63.81 mg/g at 303 K. The adsorption kinetic best fitted with pseudo second order kinetic model. The positive influence of making the addition of Ca²⁺ ions into naphthalene solution for its rapid adsorption was elucidated which is leaded by a probable increase in sorption capacity for naphthalene molecules at lower concentrations. The stable nature of crystallinity of calcium oxide and a less degree of naphthalene molecules leaching during consecutive cycles of adsorptive process and nanoparticle regeneration was also scrutinized.

Polystyrene nanofibers as an effective sorbent for the adsorption of clonazepam: kinetic and thermodynamic studies

Polystyrene (PS) electrospun nanofibers were prepared via electrospinning for the adsorption of clonazepam from aqueous solution. The adsorption conditions such as adsorption time, solution pH and the amount of adsorbent were optimized. The adsorption kinetics and thermodynamic properties of clonazepam on PS nanofibers were studied under optimized conditions. The pseudo-second-order kinetic model can fit well the adsorption process of clonazepam on polystyrene nanofibers, indicating that the diffusion process in the fiber is the rate-limiting step of the adsorption process. The adsorption equilibrium data are in accordance with the Freundlich isotherm model, and the maximum adsorption capacity is 3.2 mg g⁻¹. Thermodynamic studies revealed that the adsorption process is endothermic and spontaneous in nature. It was suggested that PS electrospun nanofibers have good potential for the separation and purification of clonazepam from a water-soluble matrix as a novel effective adsorbent material.

Polystyrene (PS) electrospun nanofibers were prepared via electrospinning for the adsorption of clonazepam from aqueous solution.

In Situ Modification of Activated Carbons by Oleic Acid under Microwave Heating to Improve Adsorptive Removal of Naphthalene in Aqueous Solutions

This study aimed to improve the adsorption capacity of activated carbon (AC) towards naphthalene (NAP) in aqueous solutions. Starch-based AC (SAC) and pulverized coal-based AC (PCAC) were prepared in a one-pot procedure by activation with oleic acid and KOH under microwave heating. Brunauer–Emmett–Teller (BET) specific surface areas reached 725.0 and 912.9 m2/g for in situ modified SAC (O-SAC1) and PCAC (O-PCAC1), respectively. π–π bond, H-bond, and hydrophobic effects were directly involved in the NAP adsorption process. Batch adsorption data were well fitted by pseudo-second order kinetics and the Freundlich isotherm model. As compared to ACs prepared with only KOH activation, NAP adsorption capacities of PCAC and SAC prepared by the one-pot method increased by 16.9% and 13.7%, respectively. Influences of varying factors were investigated in column adsorption of NAP using O-SAC1 and O-PCAC1. Based on breakthrough curves analysis, the larger column height (H), lower flow rate (Q0), and lower initial concentration (C0) resulted in the longer breakthrough and exhaustion times in both cases. Specifically, we concluded that O-PCAC1 exhibits better adsorption capacity than O-SAC1 in the given conditions. The optimized operating parameters were 1 cm (H), 1 mL/min (Q0) and 30 mg/L (C0). Finally, column adsorption data could be well fitted by the Thomas model.

Hydrothermal synthesis and microwave-assisted activation of starch-derived carbons as an effective adsorbent for naphthalene removal

In this work, starch-derived spherical carbon (HC) was prepared by hydrothermal carbonization and further activated with microwave assistance to obtain the target activated carbon (HMAC). The samples were characterized by methods of N2 adsorption-desorption, Brunauer-Emmett-Teller analysis, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, elemental analysis and scanning electron microscopy. Moreover, HMAC has a high BET surface area of 616.8 m2 g-1. The effects of initial naphthalene concentration, contact time, temperature, and pH of the naphthalene adsorbed on HC and HMAC were investigated systematically. The HMAC exhibits higher capability for naphthalene removal than HC, and the equilibrium adsorption quantity of HMAC was 223.03 mg g-1 at 303 K. The kinetic data revealed that the equilibrium time for naphthalene adsorption on samples was achieved at 40 min. The adsorption process of HC and HMAC for naphthalene both followed the pseudo-second-order kinetic and Freundlich isotherm models. Additionally, H-bond and π-π interactions were proposed to be involved in the adsorption process. An increasing adsorption amount of naphthalene onto HC and HMAC was observed when the pH value varied from 2 to 10. The HMAC can be successfully regenerated and maintained sorption performance after three cycles. This study revealed that HMAC obtained by hydrothermal synthesis combined with microwave-assisted activation has a promising application in the field of naphthalene removal.