Carbon dioxide (CO2) capture using solid sorbents has been recognized as a very promising technology that has attracted intense attention from both academic and industrial fields in the last decade. It is astonishing that around 2000 papers have been published from 2011 to 2014 alone, which is less than three years after our first review paper in this journal on solid CO2 sorbents was published. In this short period, much progress has been made and the major research focus has more or less changed. Therefore, we feel that it is necessary to give a timely update on solid CO2 capture materials, although we still have to keep some important literature results published in the past years so as to keep the good continuity. We believe this work will benefit researchers working in both academic and industrial areas. In this paper, we still organize the CO2 sorbents according to their working temperatures by classifying them as such: (1) low-temperature ( 400 °C). Since the sorption capacity, kinetics, recycling stability and cost are important parameters when evaluating a sorbent, these features will be carefully considered and discussed. In addition, due to the huge amounts of cost-effective CO2 sorbents demanded and the importance of waste resources, solid CO2 sorbents prepared from waste resources and their performance are reviewed. Finally, the techno-economic assessments of various CO2 sorbents and technologies in real applications are briefly discussed.

Recent advances in solid sorbents for CO2 capture and new development trends

A highly efficient homogeneous catalyst system for the production of CH3OH from CO2 using pentaethylenehexamine and Ru-Macho-BH (1) at 125–165 °C in an ethereal solvent has been developed (initial turnover frequency = 70 h–1 at 145 °C). Ease of separation of CH3OH is demonstrated by simple distillation from the reaction mixture. The robustness of the catalytic system was shown by recycling the catalyst over five runs without significant loss of activity (turnover number > 2000). Various sources of CO2 can be used for this reaction including air, despite its low CO2 concentration (400 ppm). For the first time, we have demonstrated that CO2 captured from air can be directly converted to CH3OH in 79% yield using a homogeneous catalytic system.

Conversion of CO2 from Air into Methanol Using a Polyamine and a Homogeneous Ruthenium Catalyst

Microfluidic devices have attracted increasing attention in the fields of biomedical diagnostics, food safety control, environmental protection, and animal epidemic prevention. Micromixing has a considerable impact on the efficiency and sensitivity of microfluidic devices. This work reviews recent advances on the passive and active micromixers for the development of various microfluidic chips. Recently reported active micromixers driven by pressure fields, electrical fields, sound fields, magnetic fields, and thermal fields, etc. and passive micromixers, which owned two-dimensional obstacles, unbalanced collisions, spiral and convergence-divergence structures or three-dimensional lamination and spiral structures, were summarized and discussed. The future trends for micromixers to combine with 3D printing and paper channel were brought forth as well.

A Review on Micromixers

Process intensification for post-combustion CO2 capture with chemical absorption: A critical review

Mixing in microfluidic devices presents a challenge due to laminar flows in microchannels, which result from low Reynolds numbers determined by the channel's hydraulic diameter, flow velocity, and solution's kinetic viscosity. To address this challenge, novel methods of mixing enhancement within microfluidic devices have been explored for a variety of applications. Passive mixing methods have been created, including those using ridges or slanted wells within the microchannels, as well as their variations with improved performance by varying geometry and patterns, by changing the properties of channel surfaces, and by optimization via simulations. In addition, active mixing methods including microstirrers, acoustic mixers, and flow pulsation have been investigated and integrated into microfluidic devices to enhance mixing in a more controllable manner. In general, passive mixers are easy to integrate, but difficult to control externally by users after fabrication. Active mixers usually take efforts to integrate within a device and they require external components (e.g. power sources) to operate. However, they can be controlled by users to a certain degree for tuned mixing. In this article, we provide a general overview of a number of passive and active mixers, discuss their advantages and disadvantages, and make suggestions on choosing a mixing method for a specific need as well as advocate possible integration of key elements of passive and active mixers to harness the advantages of both types.

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Mixing in microfluidic devices and enhancement methods

A State-of-the-Art Review of Mixing in Microfluidic Mixers

Fast extraction and enrichment of rare earth elements from waste water via microfluidic-based hollow droplet

Synthesis, characterization and CO2 capture of mesoporous SBA-15 adsorbents functionalized with melamine-based and acrylate-based amine dendrimers

Global warming and climate change due to anthropogenic carbon dioxide (CO2) have aroused significant concerns at the global scale due to rapid economic growth in industries and other fields. Therefore, CO2 capture, use, and storage have become particularly important. In this review, general background and methods for CO2 capture and separation, in particular, on ionic liquids (ILs)-based solvents and materials, are discussed. Comprehensive surveys of ILs for CO2 absorption are presented, which focused mainly on experimental researches, and then the concept is extended to functionalized absorbents and recent developments for CO2 capture. Major advantages and disadvantages of amines-based and ILs-based absorbents are discussed in this review. Solutions of traditional amines (MEA, MDEA, DEA, AMP, PZ, etc.) and ILs (conventional ILs, functionalized ILs, etc.) are summarized. Moreover, research progresses on CO2 separation are also introduced focusing mainly on amines and ILs-based membranes (e.g. supported amines membranes, SILMs). Futhermore, the fixation of CO2 into cyclic carbonates catalyzed by ILs (pure ILs, complex catalyst system with ILs, supported ILs, etc.) is summarized, clearly explaining the mechanism of CO2 fixation with ILs. Finally, exploration of some recent studies about CO2 capture and conversion by ILs and challenges for further progress are presented and related suggestions are put forward.

Yundong Wang

Papers

A State-of-the-Art Review of Mixing in Microfluidic Mixers

Fast extraction and enrichment of rare earth elements from waste water via microfluidic-based hollow droplet

Synthesis, characterization and CO2 capture of mesoporous SBA-15 adsorbents functionalized with melamine-based and acrylate-based amine dendrimers

Recent advances in carbon dioxide capture and utilization with amines and ionic liquids

Computational fluid dynamic simulation of fluid flow in a rotating packed bed