A pH- and Temperature-Responsive Magnetic Composite Adsorbent for Targeted Removal of Nonylphenol

Abstract

A pH- and temperature-responsive magnetic adsorbent [poly(N-isopropylacrylamide) grafted chitosan/Fe3O4 composite particles, CN-MCP], was synthesized for the removal of the endocrine-disrupting chemical nonylphenol. According to the structural characteristics (changeable surface-charge and hydrophilic/hydrophobic properties) of the targeted contaminant, CN-MCP was designed owning special structure (pH- and temperature-responsiveness for the changeable surface-charge and adjustable hydrophilic/hydrophobic properties, respectively). Compared to chitosan magnetic composite particles without grafting modification (CS-MCP) and several other reported adsorbents, CN-MCP exhibited relatively high adsorption capacity for nonylphenol under corresponding optimal conditions (123 mg/g at pH 9 and 20 °C; 116 mg/g at pH 5 and 40 °C). Meanwhile, high selectivity of the novel adsorbent in selective adsorption of nonylphenol from bisolute solution of nonylphenol and phenol was found. Effects of grafting ratio of the grafted polymer branches and coexisting inorganic salts on the adsorption were systematically investigated. Moreover, CN-MCP demonstrated desired reusability during 20 times of adsorption-desorption recycling. The high adsorption capacity, high selectivity, and desired reusability aforementioned revealed the significant application potential of CN-MCP in the removal of NP. On the basis of the adsorption behaviors, isotherms equilibrium, thermodynamics and kinetics studies, and instrumental analyses including X-ray photoelectron spectroscopy, BET specific surface area, zeta potential, and static water contact angle measurements, distinct adsorption mechanisms were found under various conditions: charge attraction between CN-MCP and the contaminant, as well as binding between polymeric branches of CN-MCP and nonyls, contributed to the adsorption at pH 9 and 20 °C; whereas hydrophobic interaction between CN-MCP and nonylphenol played a dominant role at pH 5 and 40 °C. The current study provided a strategy for the structural design of adsorbents according to the features of targeted emerging contaminants, and the continuity of the work was discussed and proposed.

Nitrogen Recovery from Clear-Cut Forest Runoff Using Biochar: Adsorption–Desorption Dynamics Affected by Water Nitrogen Concentration

“…The pseudofirst order model results showed that the adsorption rate, k ad , of spruce biochar decreased by increasing Q max (Table 3). The pseudo-second order kinetic model assumes that the rate-limiting step is the interaction between adsorbate and adsorbent, and it is usually used to describe chemical adsorption (Zhen et al, 2015).…”

Smart Adsorbents for Aquatic Environmental Remediation

“…A thermal and pH-responsive PNIPAM grafted COS/magnetite composite (COS-MCP), adsorbent was synthesized for the removal of nonylphenol (NNP) from water. [223] The pHresponsiveness was confirmed by the zeta potential-pH profile with a ≈9.5 isoelectric point. Under acidic conditions, the primary amino groups of pH-sensitive chitosan are positively charged, these ammonium ions then become unprotonated gradually as pH rises.…”

“…A contact angle study carried out at 20 and 40 °C proved the thermal-responsive nature of CN-MCP, with a water contact angle of 9.24° at 20 °C, that increased to 50.34° at 40 °C. [223] Thus, it could be inferred that the better adsorption performance of CN-MCP at 20 °C, was possibly due to the formation of a more hydrophilic form of NNP than at 40 °C. A slight decrease in CN-MCP particle size from 3.36 µm at 20 °C to 3.13 µm at 40 °C was due to collapsed branches, rather than extended branches of the hydrophobic PNIPAM as the temperature was above the LCST of PNIPAM (30 and 35 °C).…”

“…Fractal dimension measurements showed a reduction from 2.47 to 2.44 with rise in temperature, indicating formation of more pores during the PNIPAM branching collapsing process. [223] At pH: 9 and T: 20 °C, the adsorption of NP was governed through electrostatic attraction and ion-exchange, while at pH: 5 and T: 40°C, hydrophilic interaction between NP and PNIPAM branches on CN-MCP played a key role during NP adsorption.…”

Application of Modified Spent Mushroom Compost Biochar (SMCB/Fe) for Nitrate Removal from Aqueous Solution

“…The crystallinity of SMC, SMC/Fe, and SMCB/Fe before and after adsorption was investigated using the XRD technique, as shown in Figure 3. The composite XRD patterns include various diffraction signals at 2 thetas of 12,15,20,22,25,29,30,32,35,38,40 , and 66 • . Figure 2C shows that the XRD signals are caused by the presence of crystalline magnetic biochar on the surface of biochar.…”