On-Demand Optimization of Colorimetric Gas Sensors Using a Knowledge-Aware Algorithm-Driven Robotic Experimental Platform.

Synthesizing the best material globally is challenging; it needs to know what and how much the best ingredient composition should be for satisfying multiple figures of merit simultaneously. Traditional one-variable-at-a-time methods are inefficient; the design-build-test-learn (DBTL) method could achieve the optimal composition from only a handful of ingredients. A vast design space needs to be explored to discover the possible global optimal composition for on-demand materials synthesis. This research developed a hypothesis-guided DBTL (H-DBTL) method combined with robots to expand the dimensions of the search space, thereby achieving a better global optimal performance. First, this study engineered the search space with knowledge-aware chemical descriptors and customized multiobjective functions to fulfill on-demand research objectives. To verify this concept, this novel method was used to optimize colorimetric ammonia sensors across a vast design space of as high as 19 variables, achieving two remarkable optimization goals within 1 week: first, a sensing array was developed for ammonia quantification of a wide dynamic range, from 0.5 to 500 ppm; second, a new state-of-the-art detection limit of 50 ppb was reached. This work demonstrates that the H-DBTL approach, combined with a robot, develops a novel paradigm for the on-demand optimization of functional materials.

Preparation of a laminated structured polyethyleneimine cryogel for carbon capture.

A cryogel solid amine adsorbent with a laminated structure has been prepared by crosslinking polyethylenimine (PEI) with ethylene glycol diglycidyl ether (EGDE) at a low temperature via liquid nitrogen treatment and freeze-drying. The effects of cryogenic treatment on the morphology of the cryogels were investigated. The liquid nitrogen treatment and freeze drying were critical to create the layered structure. The fast formation of ice crystals at 77 K served as a template which directed the ordered lamellar structure of the PEI and EGDE cross-linked polymer networks. The PEI cryogel adsorbent showed excellent CO2 adsorption performance both in dry and wet conditions. In dry conditions, the PEI-gel-5-0.25 cryogel showed a 5.60 mmol/g of CO2 adsorption capacity at 75 °C. After being swelled with water, the PEI-gel-15-0.25 cryogel showed an extremely high CO2 adsorption capacity of 11.39 mmol/g at 25 °C. The adsorption behaviors of adsorbents with varied water contents were explained using kinetic simulations and intraparticle diffusion simulations. It was found that the presence of water can significantly enhance the diffusion process. The regeneration performance was examined in both dry and wet conditions. After 20 adsorption-desorption cycles, the adsorption capacity of the regenerated PEI cryogel had barely decreased, indicating reliable regeneration stability.

Preparation of a Fiber-Like 3D-Structured Adsorbent for CO2 Capture.

Solid amine adsorbents are promising materials to mitigate global warming. In this study, a commercially available melamine-formaldehyde sponge was adopted as a support to prepare a kind of solid amine adsorbent using polyethylenimine as a functional component and ethylene glycol diglycidyl ether as a cross-linker. The adsorbent, with abundant tunnels and a high amine loading amount, had a high adsorption capacity. When the amine loading was 89.6 wt%, the as-prepared adsorbent showed a high adsorption capacity of 7.29 mmol/g at 20 °C in the presence of water. The spent adsorbent could be easily regenerated by heating it at 90 °C, resulting in lower energy consumption. It has been proved by the Avrami model that physical and chemical adsorption coexist in the adsorption of CO2 on this adsorbent. Simulation with the intraparticle diffusion model has revealed that the rate-controlling step in the adsorption process was the gas film diffusion period when the adsorption temperature was below 30 °C, while it was the adsorption equilibrium period when the adsorption temperature was above 30 °C.

Preparation of a Solid Amine Microspherical Adsorbent with High CO2 Adsorption Capacity.

Amine-skeleton solid-amine materials are promising adsorbents for CO2 capture from flue gas. Here, a novel solid-amine microsphere was synthesized by cross-linking the skeleton poly(ethylenimine) (PEI) with ethylene glycol diglycidyl ether in a facile one-pot W/O emulsion system. The material had a remarkable CO2 adsorption capacity of 7.28 mmol/g in the presence of moisture at 20 °C, 0.1 bar. The highest ratio of breakthrough capacity to saturation capacity was ca. 84%. According to kinetic simulation, the Avrami kinetic model could better describe the adsorption process of CO2 under different temperatures, in which the value of R2 was above 0.99 and n was between 1 and 2, indicating that both physical and chemical adsorption mechanisms were performed during adsorption. Moreover, the material had a high swelling speed. Equilibrium was established within 30 s, and the swelling ratio was 271% at equilibrium. The saturated adsorbent could be easily regenerated with a regeneration efficiency of 94.63% after six cycles. The PEI microsphere appears to be a promising candidate material for CO2 capture from flue gas.