Vertical macro-channel modification of a flexible adsorption board with in-situ thermal regeneration for indoor gas purification to increase effective adsorption capacity

Recent Progress and Perspectives of Direct Ink Writing Applications for Mass Transfer Enhancement in Gas-Phase Adsorption and Catalysis

Conventional adsorbents and catalysts shaped by granulation or extrusion have high pressure drop and poor flexibility for chemical, energy, and environmental processes. Direct ink writing (DIW), a kind of 3D printing, has evolved into a crucial technique for manufacturing scalable configurations of adsorbents and catalysts with satisfactory programmable automation, highly optional materials, and reliable construction. Particularly, DIW can generate specific morphologies required for excellent mass transfer kinetics, which is essential in gas-phase adsorption and catalysis. Here, DIW methodologies for mass transfer enhancement in gas-phase adsorption and catalysis, covering the raw materials, fabrication process, auxiliary optimization methods, and practical applications are comprehensively summarized. The prospects and challenges of DIW methodology in realizing good mass transfer kinetics are discussed. Ideal components with a gradient porosity, multi-material structure, and hierarchical morphology are proposed for future investigations.

Adsorption film with sub-milli-interface morphologies via direct ink writing for indoor formaldehyde removal

In-situ thermally regenerated flexible adsorption films are superior for long-term purification of indoor low-concentration volatile organic compounds (VOCs). To further improve the adsorption kinetics of the films, the surface morphology of adsorption films was suggested in hierarchical channel structure. However, such structure is far from practical applications because of its complicated fabrication method and limited flexibility. In this study, we proposed a convenient and fast method named direct ink writing (DIW) based 3D printing to fabricate flexible adsorption films. Inks were prepared to have appropriate rheological properties and good printability. Three types of adsorption film (flat, straight finned, and trough-like finned) were constructed on flexible polyimide circuit substrates by DIW. We utilized the printed adsorption films for indoor level (1 ppm) formaldehyde removal. The trough-like finned film achieved the best performance among the three printed films, showing a 275% longer penetration time and 252% larger effective adsorption capacity than the flat film. By conducting a 7-cycle adsorption-desorption experiment (more than 12 h), we verified that the films' adsorption performance could effectively recover via in-situ heating. This work could dance around the complicated coating process, increase the structural flexibility and reduce the adsorbent interfacial modification cost.

Recyclable NiO/sepiolite as adsorbent to remove organic dye and its regeneration

In this study, the impregnation synthesis of NiO/sepiolite and its application for dye removal during wastewater treatment is introduced. The NiO/sepiolite materials act as an adsorbent/catalyst. It comprises a unique combination of adsorption and high-temperature gas flow regeneration (the NiO/sepiolite acts as a catalyst at this stage, using regeneration rate as evaluation index of catalytic activity of NiO/sepiolite) in a single unit, in which the NiO/sepiolite was regenerated and reused for the next round adsorption of dye. An aqueous solution of methylene blue was used to evaluate the adsorption and regeneration performance of the adsorbent/catalyst. The regeneration rate reached 74% when the reaction time and temperature were 7 min and 350 °C, respectively. The effects of the regeneration temperature and volume fraction of O₂ on the regeneration rate were investigated. And the regeneration reaction kinetics was provided. The combination of adsorptive and catalytic properties in the NiO/sepiolite composites received interesting results for removing refractory biodegradable organic pollutants. This work provides new insights for the removal of dye from wastewater using Ni catalysts supported on natural low-cost clay.

Modelling of adsorption technologies for controlling indoor air quality

Technologies for control of indoor air quality are very important to ensure that health and comfort conditions are attained in closed environments. The indoor air quality market is fertile ground for adsorption technologies, both at larger industrial scale and for residential uses. The common strategy to design adsorption technologies considers constant inlet conditions, while for most indoor air control applications, the inlet conditions will change because of the partial removal of the contaminant. This work presents a generic modelling approach, where the adsorption technology is coupled with the indoor environment to be controlled. This approach enables a tailored and more accurate process design and additionally, it can also assist in the physical location of the removal unit and sensors to control its operation. Two different examples of application of this methodology are provided: control of CO2 in tightly closed environments and "peak shaving" of water vapor in bathrooms.

A Simple Preparation Method of Graphene and TiO2 Loaded Activated Carbon Fiber and Its Application for Indoor Formaldehyde Degradation

Formaldehyde has a significant impact on human health. This study used a simple dipping method to load graphene-titanium dioxide (GR-TiO2) on activated carbon fibers (ACFs). The microstructure of GR-TiO2/ACF hybrid material was observed by SEM, combined with XRD and BET analysis. The result showed that the GR-TiO2/ACF hybrid material had a specific surface area of 893.08 m2/g and average pore size of 2.35 nm. The formaldehyde degradation efficiency of the prepared material was tested under different conditions, such as ultraviolet (UV) radiation, air supply volume, relative humidity, initial mass concentration. The results showed that the UV radiation intensity, airflow and the initial mass concentration were positively correlated with the formaldehyde removal rate, and the relative humidity was negatively correlated with the formaldehyde removal rate. The GR-TiO2/ACF hybrid material had a maximum formaldehyde removal rate of 85.54% within 120 min.

Triple combination of natural microbial action, etching, and gas foaming to synthesize hierarchical porous carbon for efficient adsorption of VOCs

Fungi residue, vinasse, and biogas residue differ from general biomass waste due to natural microbial action. Microbial fermentation helps create natural channels for the permeation of activators and produces proteins for natural nitrogen doping. Inspired by these advantages on porous carbon synthesis, this study adopted dual activators of KOH and KHCO₃ to synthesize porous carbon with different pore ratios for efficient adsorption of volatile organic compounds (VOCs). The fungi residue possessed the least lignin due to the most severe microbial action, contributing to the best pore structures after activation. The etching effect from potassium compounds and gas foaming from the carbonate decomposition contributed to creating hierarchical porous carbon with ultra-high surface area, ca. 1536.8-2326.5 m²/g. However, KHCO₃ addition also caused nitrogen erosion, such that lower adsorption capacity was attained even with a higher surface area when the mass ratio of KOH/KHCO₃ decreased from 2.5:0.5 to 2:1. The maximum adsorption capacities of chlorobenzene (CB) and benzene (PhH) reached 594.0 and 394.3 mg/g, respectively. Pore structure variations after adsorption were evaluated by freeze treatment to discover the adsorption mechanism. The surface area after CB and PhH adsorption decreased 40.3% and 34.5%, respectively. Most of the mesopores might transform into micropores due to the mono/multilayer stacking of adsorbates. The VOC adsorption kinetics were simulated by the Pseudo-first- and -second-order models and Y-N model. This paper provides a new approach for high-value biomass waste utilization after microbial action to synthesize efficient adsorbents for VOCs.

Passive Control of Indoor Formaldehyde by Mixed-Metal Oxide Latex Paints

This work reports the incorporation of mixed-metal oxides (MMOs) such as Si/Ti and Si/Zr into latex paints in the form of thin coatings for permanent trapping of indoor formaldehyde. The formaldehyde removal performance of the surface coatings was evaluated in a lab-scale indoor air chamber, and the results were compared with those of powder analogues. Due to the pore blockage by the latex, the incorporation led to 6-30% reduction in adsorption capacity and 50-70% drop in the adsorption rate for MMO-latex paints relative to their powder MMO analogues. Under the operating conditions of concentration, temperature, and relative humidity, the Si/Zr-latex paints outperformed the Si/Ti counterparts. It was also observed that performance could decrease over excessive loading, for example, Si/Zr-latex paint with 15/1 Si/Zr weight ratio showed a 20% lower adsorption capacity than that of the Si/Zr-latex paint with 25/1 Si/Zr ratio at 5 ppm_v, 25 °C, and 70% RH. While high temperature greatly reduced the adsorption rate of the MMO-latex paints, high humidity slightly promoted the rate of formaldehyde capture. In 10 L, flow-through chamber tests, 25Si/Zr-latex paint reduced 5 ppm_v formaldehyde by up to 60% at 25 °C and 70% RH with an adsorption rate of 0.34 ppm_v/h. Overall, this study highlights the potential of MMO-latex paints with optimized formation for the efficient abatement of indoor aldehydes.