[Preparation of Narrow Pore Diameter Phosphorus Containing Cotton Stalk Carbon and Its Adsorption Mechanism for Tetracycline].

Using cotton stalk as biomass raw material and phosphoric acid as a modifier, narrow pore distribution phosphorus-containing cotton stalk biochar (CSP) with a high surface area (1916 m2·g-1) and pore volume (1.3982 mL·g-1) was prepared through one-step carbonization, and the adsorption characteristics and mechanisms for tetracycline (TC) were investigated. The results showed that the TC adsorption capacity of CSP was up to 669 mg·g-1, which was 43.6 times that of unmodified cotton stalk carbon. FTIR, XPS, and isothermal adsorption studies showed that the high adsorption capacity of CSP for TC resulted from the joint action of complexation, hydrogen bonding, pore filling, and π-π dispersion forces, and the highly active phosphate ester group (P-O-C) endowed by phosphoric acid modification greatly enhanced the chemical interaction with TC molecules, which was the key factor for the significant increase in adsorption capacity. Isotherm and thermodynamic study further confirmed that chemical adsorption played a major role in the adsorption process, the adsorption process was spontaneous and endothermic, and the material had good regeneration performance. This study provides theoretical guidance for the preparation of modified biomass carbon with high adsorption performance to remove tetracycline antibiotic pollution.

[Preparation of High Specific Surface Thiourea Modified Peanut Shell Carbon and Adsorption of Tetracycline and Copper].

High activity nitrogen and sulfur co-doping high specific surface-modified peanut shell carbon PBC-NS was prepared through one-step carbonization using thiourea and phosphoric acid as modifiers. The TC/Cu(Ⅱ) adsorption characteristics of peanut shell carbon in single and mixed-adsorption systems were discussed, and the enhancement effect and mechanism of modification on TC/Cu(Ⅱ) adsorption were studied. The results showed that the modified peanut shell carbon PBC-NS successfully introduced nitrogen-sulfur functional groups such as Pyridinic N, Graphitic N, C- S-C, and -SH, and the modified specific surface area was as high as 1437 m2·g-1, which was 2.6 times higher than that before modification. The maximum adsorption capacities of modified peanut shell carbon PBC-NS for single-system TC and Cu(Ⅱ) were 585 mg·g-1 and 21.2 mg·g-1, respectively, which were 2.6 times and 2.7 times higher than those before modification. The saturated adsorption capacities of TC and Cu(Ⅱ) in the system were increased by 13 mg·g-1 and 6.8 mg·g-1 compared with that in the single system. The adsorption capacity of PBC-NS for TC and Cu(Ⅱ) could still reach 66% and 70% of the initial adsorption capacity after four times of repeated use. Isotherm fitting and modern spectroscopic analysis indicated that the substantial increase in the adsorption capacity of TC/Cu(Ⅱ) on PBC-NS by modification was mainly attributed to the combined effect of chemical chelation of nitrogen-sulfur active functional sites and pore filling caused by high specific surface area. These results indicated that thiourea/phosphoric acid chemical modification could effectively improve the adsorption capacity of peanut shell carbon for TC/Cu(Ⅱ), which can provide a new idea for the structural regulation of mixed-pollution biochar with high adsorption capacity and adsorption treatment of TC/Cu(Ⅱ) water pollution.

[Adsorption kinetics and mechanism of lead (II) on polyamine-functionalized mesoporous activated carbon].

Bagasse mesoporous carbon was prepared by microwave assisted H3 PO4 activation. Amido and imido groups were modified with ethanediamine on the channels' surface of mesoporous carbon through nitric oxidation and amide reaction. The influence of Pb(II) concentration, adsorption time on Pb(II) adsorption on the ethanediamine-modified mesoporous carbon (AC-EDA) was investigated. The adsorption kinetics and mechanism were also discussed. The results showed that AC-EDA had a great performance for Pb(II) adsorption, and more than 70% of Pb(II) was adsorbed in 5 minutes. The adsorption amount of Pb(II) on the carbon increased with the increase of solution pH in acidic conditions. It was found that AC-EDA had different binding energies on different adsorption sites for Pb(II) separation. The Pb(II) adsorption process on AC-EDA was controlled by intra-particle diffusion in the first 3 min, and then film diffusion played the important pole on the adsorption. The adsorption amount increased with the increase of temperature, indicating the adsorption was an endothermic reaction. The high adsorption energy (> 11 kJ x mol(-1)) implied that the) adsorption was a chemical adsorption. The XPS of AC-EDA before and after Pb(II) adsorption showed that the polyamine group was involved in the adsorption, and should be a main factor of the high efficient adsorption.

[Preparation, characterization and adsorption performance of mesoporous activated carbon with acidic groups].

Mesoporous activated carbons containing acidic groups were prepared with cotton stalk based fiber as raw materials and H3PO4 as activating agent by one step carbonization method. Effects of impregnation ratio, carbonization temperature and heat preservation time on the yield, elemental composition, oxygen-containing acid functional groups and adsorptive capacity of activated carbon were studied. The adsorption capacity of the prepared activated carbon AC-01 for p-nitroaniline and Pb(II) was studied, and the adsorption mechanism was also suggested according to the equilibrium experimental results. The maximum yield of activated carbons prepared from cotton stalk fiber reached 35.5% when the maximum mesoporous volume and BET surface area were 1.39 cm3 x g(-1) and 1 731 m2 x g(-1), respectively. The activated carbon AC-01 prepared under a H3 PO4/precursor ratio of 3:2 and activated at 900 degrees C for 90 min had a total pore volume of 1.02 cm3 x g(-1), a micoporous ratio of 31%, and a mesoporous ratio of 65%. The pore diameter of the mesoporous activated carbon was mainly distributed in the range of 2-5 nm. The Langmuir maximum adsorption capacities of Pb(II) and p-nitroaniline on cotton stalk fiber activated carbon were 123 mg x g(-1) and 427 mg x g(-1), respectively, which were both higher than those for commercial activated carbon fiber ACF-CK. The equilibrium adsorption experimental data showed that mesopore and oxygen-containing acid functional groups played an important role in the adsorption.

[Preparation, characterization and adsorption performance of high surface area biomass-based activated carbons].

High surface area activated carbons were prepared with Spartina alterniflora and cotton stalk as raw materials and KOH as activating agent. Effects of materials type, impregnation ratio, activation temperature and heat preservation time on the yield, elemental composition and adsorptive capacity of activated carbon were studied. The properties and pore structure of the carbons were characterized with nitrogen adsorption, powder X-ray diffractometry (XRD), infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Main pore characteristics of activated carbons were analyzed by BET equation, Horvath-Kawazoe BET method and DFT method. The considerable preparation conditions are obtained as follows: impregnation ratio of 3: 1, an activation temperature of 800 degrees C and an activation time of 1.5 h. The BET surface area of activated carbon prepared from Spartina alterniflora reached 2 825 m2 x g(-1) when its total pore volume, yield, iodine number and methylene blue adsorption were 1.374 cm3 x g(-1), 16.36%, 1797 mg x g(-1) and 495 mg x g(-1) respectively under above conditions. The activated carbon from cotton stalk was prepared with BET surface area of 2 135 m2 x g(-1), total pore volume of 1.038 cm3 x g(-1), yield of 11.22%, methylene blue adsorption of 1 251 mg x g(-1), and iodine number of 478 mg x g(-1), respectively. The methylene blue adsorption and iodine number are much higher than the national first level for activated carbon. The Langmuir maximum adsorption capacities of 2,4-dinitrophenol on the two carbons were 932 mg x g(-1) and 747 mg x g(-1), respectively, which are superior to ordinary activated carbon and activated carbon fiber.

Transplantation of a hydrogen bonding network from West Nile virus protease onto Dengue-2 protease improves catalytic efficiency and sheds light on substrate specificity.

The two-component serine protease of flaviviruses such as Dengue virus (DENV) and West Nile virus (WNV) are attractive targets for inhibitor/therapeutic design. Peptide aldehyde inhibitors that bind to the covalently tethered two-component WNV protease (WNVpro) with 50% inhibitory concentration (IC(50)) at sub-micromolar concentrations, bind the equivalent DENV-2 protease (DEN2pro) with IC(50) of micromolar concentrations at best. Conversely, the protease inhibitor aprotinin binds DEN2pro ∼1000-fold more tightly than WNVpro. To investigate the residues that are crucial for binding specificity differences, a binding-site network of hydrogen bonds was transplanted from WNVpro onto DEN2pro. The transplantations were a combination of single, double and triple mutations involving S79D, S83N and S85Q. The mutant DENV proteases, except those involving S85Q, proved to be more efficient enzymes, as measured by their kinetic parameters. The binding affinities of the mutants to peptide inhibitors however showed only marginal improvement. Protein structure modeling suggests that the negatively charged residue cluster, Glu89-Glu92, of the NS2B cofactor may play an important role in determining substrate/inhibitor-binding specificity. These same residues may also explain why aprotinin binds more tightly to DEN2pro than WNVpro. Our results suggest that structure-based inhibitor design experiments need to explicitly consider/include this C-terminal region whose negative charge is conserved across the four DENV serotypes and also among the flavivirus family of proteases.

[Adsorption behavior and influence factors of p-nitroaniline on high surface area activated carbons prepared from plant stems].

Low-cost and high surface area microporous activated carbons were prepared from Spartina alternilora and cotton stalk with KOH activation under the conditions of impregnation ratio of 3.0, activation temperature at 800 degrees C and activation time of 1.5 h. The adsorption behavior of p-nitroaniline on the activated carbons was investigated by batch sorption experiments. The influences of solution pH value, adsorbent dose and temperature were investigated. The adsorption isotherm and thermodynamic characteristics were also discussed. The Spartina alterniflora activated carbon (SA-AC) has a high surface area of 2825 m2 x g(-1) and a micropore volume of 1.192 cm3 x g(-1). The BET surface area and micropore volume of the cotton stalk activated carbon (CS-AC) are 2135 m2 x g(-1) and 1.011 cm3 x g(-1), respectively. The sorption experiments show that both the activated carbons have high sorption capacity for p-nitroaniline. The Langmuir maximum sorption amount was found to be 719 mg x g(-1) for SA-AC and 716 mg x g(-1) for CS-AC, respectively. The sorption was found to depend on solution pH, adsorbent dose, and temperature. The optimum pH for the removal of p-nitroaniline was found to be 7.0. The Freundlich model and Redlich-Peterson model can describe the experimental data effectively. The negative changes in free energy (delta G0) and enthalpy (delta H0) indicate that the sorption is a spontaneous and exothermic procedure. The negative values of the adsorption entropy delta S0 indicate that the mobility of p-nitroaniline on the carbon surface becomes more restricted as compared with that of those in solution.

[Adsorption kinetic and thermodynamic studies of lead onto activated carbons from cotton stalk].

Low-cost high surface area microporous carbons were prepared from cotton stalk and cotton stalk fiber by H3PO4 activation. The adsorption of lead ions on the carbons was investigated by conducting a series of batch adsorption experiments. The influence of solution pH value, contact time and temperature was investigated. The adsorption kinetics, thermodynamic behavior and mechanism were also discussed. The surface area and pore structure of the activated carbons were analyzed by BET equation, BJH method and H-K method according to the data from nitrogen adsorption at 77K. Boehm titration, Fourier transform infrared spectroscopy (FTIR), the point of zero charge (pH(PZC)) measurement and elemental analysis were used to characterize the surface properties. The results show that the carbons from cotton stalk and cotton stalk fiber have high surface area of 1570 and 1731 m2 x g(-1), and high content of oxygen-containing functional groups of 1.43 and 0.83 mmol x g(-1). The adsorption experiments show that the carbons have high adsorption capacity for lead, and the maximum adsorption equilibrium amount was found to be 120 mg x g(-1). The adsorption amount increased with contact time, and almost 80% of the adsorption occurred in the first 5 min. The pseudo-second-order model describes the adsorption kinetics most effectively. The Freundlich isotherm was found to the best explanation for experimental data. The negative change in free energy (delta G0) and positive change in enthalpy (delta H0) indicate that the adsorption is a spontaneous and endothermic process, and the adsorption of lead ions onto the carbons might be involved in an ion-exchange mechanism.