Enhanced removal of organophosphate esters by iron-modified biochar with developed mesoporous: Performance and mechanism based on site energy distribution theory

Removing the widely concerned pollutant of organophosphate esters (OPEs) by agriculture waste biochar is an effective way to address the waste and pollutant problem simultaneously. In this work, an iron-modified coconut shell biochar (MCSB) was prepared by co-pyrolysis method and used to adsorb tris(2-chloroethyl) phosphate (TCEP) and tris(1-chloro-2-propyl) phosphate (TCPP), which were two typical OPEs. The attention was focused on comprehensively investigating the adsorption behaviors to study the adsorption mechanisms of TCEP and TCPP onto MCSB. With the development of mesoporous and formation of γ-Fe₂O₃ in MCSB, the adsorption equilibrium was quickly reached in 60 min with the Langmuir maximum adsorption capacities of 211.3 mg/g for TCEP and 223.7 mg/g for TCPP, respectively. Results of adsorption kinetics and isotherm showed the heterogeneous and multilayer of the adsorption process. Pore-filling interaction, the Lewis acid-base interaction, and the hydrophobic interaction were considered to drive the adsorption. And the site energy distribution theory was introduced to further reveal that the physisorption was the main adsorption mechanism, while the Lewis acid-base interaction was responsible for the differences in adsorption of TCEP and TCPP onto MCSB. Additionally, the excellent adsorption performances of MCSB in various circumstances and fixed-bed column experiments suggested that the MCSB would be a promising adsorbent for OPEs removal.

A mechanistic study on removal efficiency of four antibiotics by animal and plant origin precursors-derived biochars

Extensive research has been performed on the utilization of biochar for pollutant removal via sorption. Additionally, the relationship between sorption strength of organic pollutants by organic matter and nanomaterials and their sorption site energy distribution has been studied. However, the linkage between removal efficiency of organic pollutants and the sorption site energy distribution on biochars is unknown. As a first attempt to address this knowledge gap, three biochars were derived from two plant-origin precursors (corn straw-CS; birch sawdust-BS) and one animal-origin precursor (meat and bone meal-MBM) at 500 °C (CS-500, BS-500, and MBM-500). In addition, two biochars were prepared with CS at 300 and 800 °C (CS-300 and CS-800) to examine the relationship between their site energy distribution and removal efficiency of antibiotics including sulfadiazine (SDZ), sulfamethoxazole (SMX), tetracycline (TC) and ciprofloxacin (CFX) by these materials. Our findings showed that the antibiotic-biochar interactions can be well interpreted with site energy distribution and XPS analysis results. Polar interactions between CS-300, CS-500, and CS-800 and SDZ and SMX occurring at the high-energy sites dominated their removal. However, TC and CFX removal by these biochars was driven by their polar interactions occurring at high-energy sites and π-π interactions at low-energy sites. The π-π stacking mechanism tended to dominate their removal with increasing charring temperature. Abundance of polar functionalities on CS-500, BS-500, and MBM-500 and TC removal efficiency of these materials consistently followed an order of MBM-500 > CS-500 > BS-500, highlighting importance of precursors for making biochars and polar interactions in its removal.

Effect of dissolved organic matter on adsorption of sediments to Oxytetracycline: An insight from zeta potential and DLVO theory

To reveal the adsorption mechanism of sediment to antibiotics with the presence of dissolved organic matter (DOM), batch experiments were carried out by oxytetracycline (OTC) on sediments with decayed plants (PDOM) and composted chicken manure (MDOM), and the zeta potential in the system before and after adsorption was measured. Results showed that the PDOM promoted the adsorption process, while the MDOM inhibited the adsorption. Adding PDOM, the change of zeta potential (Δζ) increased by 40.08% for first terrace sediments (FT) and 63.98% for riverbed sediments (RB), respectively; meanwhile, MDOM decreased by 20.04% for FT and 28.39% for RB, respectively. The results of kinetic fitting models of replacing the adsorption amount with Δζ were consistent with the initial. It indicated that there was a positive correlation between the adsorption amount and Δζ, and the zeta potential can be used to quickly judge the degree of adsorption process. The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory describes the interactions of sediment particles. In terms of adsorption amount, zeta potential (absolute value) and total interaction energy all followed the order: RB > FT, RB-PDOM > FT-PDOM, and RB-MDOM > FT-MDOM. The more negative the zeta potential is, the better the dispersion of the particles is. Stronger repulsion is more conducive to adsorbing positively charged OTC. The site energy distribution theory further explained that the distribution of adsorption site in the various states of sediments increased while adding the PDOM and decreased while adding the MDOM.

Analysis of 17α-ethinylestradiol and bisphenol A adsorption on anthracite surfaces by site energy distribution

17α-Ethinylestradiol (EE2) and bisphenol A (BPA) are highly toxic and widely detected endocrine-disrupting compounds (EDCs) throughout the world in surface waters. Adsorption is an effective way to remove EE2 and BPA from water. However, it is difficult to clearly explain the mechanism of adsorption theoretically only through classic adsorption models. In order to insight into the adsorption of EE2 and BPA, site energy distribution (SED) theory was introduced to investigate the adsorption of EE2 and BPA on heterogeneous surfaces. EE2 and BPA were adsorbed on un-anthracite (unmodified anthracite) and 4K anthracite (4 mol L^-1 KOH-modified anthracite) in single- and bi-component systems under various temperatures and pHs. The results suggested that EE2 and BPA molecules first occupied the high-energy adsorption sites and then spread to low-energy adsorption sites. There were more high-energy sites on 4K anthracite, resulting in a higher adsorption capability for EE2 and BPA. Besides, increasing temperature and acidic environment were conducive to the EE2 and BPA adsorption. SED analyses indicated that, in neutral solutions, π-π electron donor-acceptor (EDA) interaction might be the primary mechanism for BPA adsorption, while ligand exchange, hydrogen bonds, and π-π EDA interaction might simultaneously work in the adsorption of EE2. It was possible that EE2 molecule was near perpendicular to surface, while BPA molecule was parallel to surface, resulting in the higher adsorption capacities of EE2. However, compared with EE2, BPA had outstanding competitive advantages in bi-component system because of the stronger π-π EDA interaction between BPA and anthracite.

High-resolution insight into the competitive adsorption of heavy metals on natural sediment by site energy distribution

Investigating competitive adsorption on river/lake sediments is valuable for understanding the fate and transport of heavy metals. Most studies have studied the adsorption isotherms of competitive heavy metals, which mainly comparing the adsorption information on the same concentration. However, intrinsically, the concentration of each heavy metal on competitive adsorption sites is different, while the adsorption energy is identical. Thus, this paper introduced the site energy distribution theory to increase insight into the competitive adsorption of heavy metals (Cu, Cd and Zn). The site energy distributions of each metal with and without other coexisting heavy metals were obtained. It illustrated that site energy distributions provide much more information than adsorption isotherms through screening of the full energy range. The results showed the superior heavy metal in each site energy area and the influence of competitive metals on the site energy distribution of target heavy metal. Site energy distributions can further help in determining the competitive sites and ratios of coexisting metals. In particular, in the high-energy area, which has great environmental significance, the ratios of heavy metals in the competitive adsorption sites obtained for various competitive systems were as follows: slightly more than 3:1 (Cu-Cd), slightly less than 3:1 (Cu-Zn), slightly more than 1:1 (Cd-Zn), and nearly 7:2:2 (Cu-Cd-Zn). The results from this study are helpful to deeply understand competitive adsorption of heavy metals (Cu, Cd, Zn) on sediment. Therefore, this study was effective in presenting a general pattern for future reference in competitive adsorption studies on sediments.