Zhanquan Zhang

Sustainable and hierarchical porous Enteromorpha prolifera based carbon for CO2 capture.

Nitrogen-containing porous carbon was synthesized from an ocean pollutant, Enteromorpha prolifera, via hydrothermal carbonization and potassium hydroxide activation. Carbons contained as much as 2.6% nitrogen in their as-prepared state. Physical and chemical properties were characterized by XRD, N(2) sorption, FTIR, SEM, TEM, and elemental analysis. The carbon exhibited a hierarchical structure with interconnected microporosity, mesoporosity and macroporosity. Inorganic minerals in the carbon matrix contributed to the development of mesoporosity and macroporosity, functioning as an in situ hard template. The carbon manifested high CO(2) capacity and facile regeneration at room temperature. The CO(2) sorption performance was investigated in the range of 0-75°C. The dynamic uptake of CO(2) is 61.4 mg/g and 105 mg/g at 25°C and 0°C, respectively, using 15% CO(2) (v/v) in N(2). Meanwhile, regeneration under Ar at 25°C recovered 89% of the carbons initial uptake after eight cycles. A piecewise model was employed to analyze the CO(2) adsorption kinetics; the Avrami model fit well with a correlation coefficient (R(2)) of 0.98 and 0.99 at 0°C and 25°C, respectively.

Adsorption and destruction of PCDD/Fs using surface-functionalized activated carbons

Activated carbon adsorbs polychlorinated dibenzo-p-dioxins and -furans (PCDD/Fs) from gas streams but can simultaneously generate PCDD/Fs via de novo synthesis, increasing an already serious disposal problem for the spent sorbent. To increase activated carbons PCDD/F sorption capacity and lifetime while reducing the impact of hazardous waste, it is beneficial to develop carbon-based sorbents that simultaneously destroy PCDD/Fs while adsorbing the toxic chemicals from gas streams. In this work, hydrogen-treated and surface-functionalized (i.e., oxygen, bromine, nitrogen, and sulfur) activated carbons are tested in a bench-scale reactor as adsorbents for PCDD/Fs. All tested carbons adsorb PCDD/F efficiently, with international toxic equivalent removal efficiencies exceeding 99% and mass removal efficiencies exceeding 98% for all but one tested material. Hydrogen-treated materials caused negligible destruction and possible generation of PCDD/Fs, with total mass balances between 100% and 107%. All tested surface-functionalized carbons, regardless of functionality, destroyed PCDD/Fs, with total mass balances between 73% and 96%. Free radicals on the carbon surface provided by different functional groups may contribute to PCDD/F destruction, as has been hypothesized in the literature. Surface-functionalized materials preferentially destroyed higher-order (more chlorine) congeners, supporting a dechlorination mechanism as opposed to oxidation. Carbons impregnated with sulfur are particularly effective at destroying PCDD/Fs, with destruction efficiency improving with increasing sulfur content to as high as 27%. This is relevant because sulfur-treated carbons are used for mercury adsorption, increasing the possibility of multi-pollutant control.

Clover leaf-shaped Al2O3 extrudate as a support for high-capacity and cost-effective CO2 sorbent

Amine-functionalized clover leaf-shaped Al(2)O(3) extrudates (CA) were prepared for use as CO(2) sorbent. The as-synthesized materials were characterized by N(2) adsorption, XRD, SEM and elemental analysis followed by testing for CO(2) capture using simulated flue gas containing 15.1% CO(2). The results showed that a significant enhancement in CO(2) uptake was achieved with the introduction of amines into CA materials. A remarkably high volume-based capacity of 70.1mg/mL of sorbent of this hybrid material suggests that it can be potentially used for CO(2) capture from flue gases and other stationary sources, especially those with low CO(2) concentration. The novel adsorbent reported here performed well during prolonged cyclic operations of adsorption-desorption of CO(2).

Effects of dissolution alkalinity and self-assembly on ZSM-5-based micro-/mesoporous composites: a study of the relationship between porosity, acidity, and catalytic performance

ZSM-5-based micro-/mesoporous composites have attracted extensive attention as a promising material that could be industrialized in the near future. The hierarchical structure and catalytic performance of the ZSM-5-based hierarchical composite are highly dependent on its treatment conditions. Of these synthesis parameters, dissolution alkalinity is the most important one. However, systematic studies on the effects of dissolution alkalinity, specifically those that discuss the relationship between porosity, acidity, and catalytic performance in ZSM-5-based hierarchical composites by the combined dissolution and self-assembly method, have not yet been reported. In this article, the porosity and acidity of ZSM-5-based micro-/mesoporous composite samples made by select dissolution alkalinities are systematically investigated. Various characterization techniques illustrate that three different groups of ZSM-5-based micro-/mesoporous composites are classified based on their distinctive indexed hierarchical factor values, I through III. Group I, treated with 0 to 0.5 mol L−1 NaOH, is mesoporous ZSM-5 attached by Al-MCM-41-like ordered mesostructures and has a high yield for liquid petroleum gas. Group II, treated with 0.5 mol L−1 to 1.0 mol L−1 NaOH, is a mixture of ZSM-5 zeolite phase and Al-MCM-41-like ordered mesostructure phase and has a high yield of light oil. Group III, treated with 1.0 mol L−1 NaOH, is formed by complete collapse of ZSM-5 crystals and formation of Al-MCM-41-like ordered mesostructures and exhibits a high yield of total liquid oil. Due to increasingly enhanced accessibility of acid sites (indexed as accessibility index), all three groups of ZSM-5-based micro-/mesoporous composites show comparable conversion for vacuum gas oil cracking compared with their parent counterpart. These results are of vital importance during the selection of the synthesis conditions and scale-up tests of ZSM-5-based micro-/mesoporous composites to selectively produce liquid petroleum gas, light oil, and total liquid oil.