Effect of double carbon chains on enhanced removal of phenol from wastewater by amphoteric-gemini complex-modified bentonite.

A novle amphoteric-gemini complex-modified bentonite was prepared with a gemini surfactant ethylene bis (tetradecyl dimethyl ammonium chloride) (EB) on the basis of the bentonite modified by amphoteric modifier dodecyldimethyl betaine (BS). The surface and structural characteristics of modified bentonite were characterized by X-ray diffraction (XRD), specific surface area (SBET), scanning electron microscopy (SEM), Fourier infrared spectroscopy (FTIR), total carbon (TC) and total nitrogen (TN). In addition to studying the enhanced effect of gemini surfactants on phenol adsorption by kinetics and equilibrium adsorption, the influences of modification ratio, pH, temperature and ionic strength were investigated. Results showed that BS + EB complex modification increased the interlayer spacing (IS), TC and TN of bentonite (BT), and SBET decreased with the increase in its total modification ratio. The adsorption of phenol on modified bentonite reached equilibrium in 20 min, and the adsorption capacities were in the order of BS+50 EB (BS+50% CEC EB)>BS+100 EB > BS+150 EB > BS+25 EB > BS > BT. The adsorption capacities of phenol on BS + EB complex modified bentonite (CMB) increased by 9.98-15.96 and 1.19-3.35 times compared with those on BT and BS single modified bentonite (SMB), respectively. The phenol adsorption capacities decreased with the increases in temperature and pH, while it increased with the augment in ionic strength. This study revealed that double carbon chains increased the organic carbon content more effectively than single carbon chains at low complex modification ratios, thus promoting the adsorption of phenol by hydrophobic partitioning on the bentonite surface.

Co-adsorption capabilities and mechanisms of bentonite enhanced sludge biochar for de-risking norfloxacin and Cu2+ contaminated water.

Various bentonite-sludge biochar composites were fabricated by a sequence of loading and pyrolysis for the simultaneous removal of norfloxacin (NOR) and copper (Cu2+) from an aqueous solution. The morphology and characteristics of obtained composites were reflected through cation exchange capacity (CEC), BET specific surface area (SBET), SEM, XRD, FTIR and XPS. The isothermal adsorption results showed that Sips adsorption model fitted better for the adsorption of NOR and Cu2+ during co-adsorption. The theoretical maximum adsorption capacity of BT:2 SB (the mass ratio of bentonite to sludge is 1:2) for NOR and Cu2+ was 89.36 mg g-1 and 104.10 mg g-1 at 25 °C in the co-adsorption system. The thermodynamic results showed the capture of NOR and Cu2+ was spontaneous, accompanied by an endothermic reaction with different randomness. In the co-adsorption system, the two were antagonistic to each other due to competition for the adsorption sites of hydroxyl, carboxylic acid and negatively charged provided by bentonite-sludge biochar. This study suggests that using natural mineral as a pyrolysis improver for sludge biochar can product the value-enhanced biochar for simultaneous removal of antibiotic and metal contaminants.

[Adsorption of BS-18 Amphoterically Modified Bentonite to Tetracycline and Norfloxacin Combined Pollutants].

Antibiotic pollution in the environment has become a hot topic. The amphoteric surfactant octadecyl dimethyl betaine (BS-18) was adopted to modify bentonite to investigate the effects and mechanisms of the composite adsorption of different types of antibiotics. Under the different modification ratios, temperatures, pH values, and ionic strength conditions, the adsorption of tetracycline (TC) and norfloxacin (NOR) by bentonite was studied under single and compound conditions, and the adsorption mechanism was analyzed and discussed in combination with the surface properties of amphoterically modified bentonite. The results showed that compared with those of CK, the CEC and specific surface area of the soil samples modified by BS-18 decreased, whereas the total carbon and total nitrogen contents increased. The adsorption order of BS-18 amphoterically modified bentonite to TC was CK > 100BS > 25BS > 50BS, which was in accordance with the Langmuir model; the adsorption order of NOR was 25BS > 50BS > CK > 100BS, which was consistent with the Henry model. The adsorption capacity of TC and NOR in the TC and NOR composite system was higher than that in the single system. With the increase in temperature, the adsorption of amphoterically modified bentonite to TC showed a positive warming effect, whereas the adsorption of NOR declined as the temperature increased. When the ionic strength increased from 0.001 mol·L-1 to 0.500 mol·L-1, the adsorption of TC and NOR on each soil sample was inhibited. The pH of the solution can affect the existing forms of TC and NOR, and the adsorption capacity showed different trends as the pH increased. The adsorption of TC by BS-18-modified bentonite was mainly caused by electric charge attraction, whereas the adsorption of NOR was mainly caused by the combination of electric charge attraction and the hydrophobic effect. The different values of the octanol/water partition coefficient and the difference in structure resulted in different adsorption modes. In the TC and NOR composite system, a TC+NOR mixture was formed to promote the adsorption of soil samples.

Co-existing TiO2 nanoparticles influencing adsorption/ desorption of tetracycline on magnetically modified kaolin.

Interaction of coexisting nanoparticles (NPs) and other pollutants may affect their behavior in the environment. In this study, we investigated the effects of TiO2 NPs on the adsorption and desorption of tetracycline (TC) by magnetized kaolin (MK). The interactions among TC, TiO2 NPs, and MK were then discussed through their morphology and characteristics by using scanning electron microscopy, X-ray energy dispersive spectrometry, Transmission electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy analyses. Results showed that TiO2 NPs increased TC adsorption on MK by 2.02% and increased TC desorption by 45.26%, TC increased the maximum adsorption of TiO2 on MK from 31.32 to 49.42 mg g-1 and decreased the amount of stable adsorption state TiO2 NPs on MK from 17.92 to 12.71 mg g-1. The characterization results demonstrated that TC molecules combined on MK though hydrogen bonding, π-π bonding and hydrophobic interaction. The adsorption of TiO2 NPs on MK can provide additional hydrogen-bonding sites for TC adsorption by increasing the number of hydroxyl groups. However, TC can decrease the electrostatic attraction sites for TiO2 NPs adsorption on the MK surface. The complexation of TC and TiO2 NPs weakened the electrical attraction between MK and TiO2 NPs and decreased the amount of stable adsorption state TiO2 NPs.

Comparison of Cd2+ adsorption onto amphoteric, amphoteric-cationic and amphoteric-anionic modified magnetic bentonites.

Organic-magnetic bentonites (OMBts), i.e., amphoteric modified MBt (BS-MBt), amphoteric-cationic modified MBt (BS-CT-MBt) and amphoteric-anionic modified MBt (BS-SDS-MBt), obtained by modifying magnetic bentonite (MBt) with amphoteric surfactant (BS), cationic surfactant (CT) and anionic surfactant (SDS) were investigated with the aim to remove cadmium (Cd2+). The modifier contents, surface charge and Cd2+ adsorption performances of OMBts were compared, and the influences of pH, temperature and ionic strength on Cd2+ removal were evaluated. Results showed that modifier contents of OMBts increased in the order: BS-CT-MBt > BS-MBt > BS-SDS-MBt. Although CEC of adsorbents increased in the order: MBt > BS-MBt > BS-SDS-MBt > BS-CT-MBt. The BS-MBt exhibited the highest Cd2+ adsorption capacity (233.19 mmol kg-1) than other adsorbents. The adsorption isotherms could be well described by Langmuir model. The Cd2+ adsorption capacities on MBt and OMBts increased with an increase in pH, temperature and with a decrease of ionic strength. According to characterizations (FT-IR and XPS) and experiments, Cd2+ adsorption on MBt and OMBts most possibly involved electrostatic interaction, ion exchange, and surface complexation. Furthermore, the adsorption of Cd2+ on BS-MBt was also attributed to the chelation. The amidocyanogen group of BS-CT-MBt inhibited adsorption of Cd2+ due to electrostatic repulsion, while Cd2+ was adsorbed on BS-SDS-MBt through electrostatic attraction induced by the sulfo group.