Metal-organic frameworks (MOFs) are a new class of microporous materials that possess framework flexibility, large surface areas, “tailor-made” framework functionalities, and tunable pore sizes. These features empower MOFs superior performances and broader application spectra than those of zeolites and phosphine-based molecular sieves. In parallel with designing new structures and new chemistry of MOFs, the observation of unique breathing behaviors upon adsorption of gases or solvents stimulates their potential applications as host materials in gas storage for renewable energy. This has attracted intense research energy to understand the causes at the atomic level, using in situ X-ray diffraction, calorimetry, Fourier transform infrared spectroscopy, and molecular dynamics simulations. This article is developed in the following order: first to introduce the definition of MOFs and the observation of their framework flexibility. Second, synthesis routes of MOFs are summarized with the emphasis on the hydrothermal synthesis, owing to the environmental-benign and economically availability of water. Third, MOFs exhibiting breathing behaviors are summarized, followed by rationales from thermodynamic viewpoint. Subsequently, effects of various functionalities on breathing behaviors are appraised, including using post-synthetic modification routes. Finally, possible framework spatial requirements of MOFs for yielding breathing behaviors are highlighted as the design strategies for new syntheses.

Over the past decades, organic-inorganic hybrid polymers have been applied in different fields, including the adsorption of pollutants from wastewater and solid-state separations. In this review, firstly, these compounds are classified. These compounds are prepared by sol-gel method, self-assembly process (mesopores), assembling of nanobuilding blocks (e.g., layered or core-shell compounds) and as interpenetrating networks and hierarchically structures. Lastly, the adsorption characteristics of heavy metals of these materials, including different kinds of functional groups, selectivity of them for heavy metals, effect of pH and synthesis conditions on adsorption capacity, are studied.

Small-angle X-ray scattering (SAXS) has been used to quantify how perturbations of the tetrapropylammonium (TPA) cation structure affect the growth of silicalite-1 from clear solutions at 368 K. Alkyltripropylammonium (RN(C3H7)3 +OH-, R = Me, Et, Bu, and Pe), dialkyldipropylammonium (R2N(C3H7)2 +OH-, R = Et and Bu), and bis-1,6-(tripropylammonium)hexamethylene dihydroxide (TPA-dimer) cations are used as structure-directing agents (SDAs) to synthesize silicalite-1 from clear solution mixtures comparable to those that have been previously investigated for the TPAOH mediated synthesis (i.e., 1 TEOS:0.36 TPAOH:20 H2O, 368 K). All mixtures studied except those employing dialkyldipropylammonium cations lead to the formation of silicalite-1. The in-situ SAXS investigations show that TPA cations lead to the shortest reaction time as indicated by the observance of Bragg diffraction peaks (15 approximately 16.5 h) and the largest particle growth rate (1.9 +/- 0.1 nm/h). Substituting a propyl group of the TPA moiety with a different alkyl group significantly affects silicalite-1 nucleation and growth with the trend Bu > Et > Pe > Me. Synthesis mixtures containing the TPA-dimer also show a slower growth rate. All the solutions show a bimodal particle distribution throughout zeolite growth with the primary particle size being approximately 5 nm in all cases, independent of the SDA identity. Syntheses using diethyldipropylammonium hydroxide, dibutyldipropylammonium hydroxide, and 4,4'-trimethylenebis(1-methyl-1-hexyl-piperidinium) dihydroxide as the SDA do not result in silicalite-1 formation, showing that the nucleation of silicalite-1 from clear solution at 368 K is sensitive to the SDA geometry.

Synthesis of three-dimensional anisotropic microparticles using a simple one-step microfluidic-based method is described. The method exploits the nonuniformity of the polymerizing UV light, UV absorption by opaque nanoparticles in the precursor solution, and discontinuous photomask patterns to make magnetic and non-magnetic microparticles in a twodimensional microchannel. Numerical simulations of monomer conversion in the microfluidic channel are performed to predict the manufactured particle shape.

In situ small-angle X-ray scattering (SAXS) is used to investigate the influence of alcohol identity and content on silicalite-1 growth from clear solutions at 368 K. Several tetraalkyl orthosilicates (Si(OR)4, R = Me, Pr, and Bu) are used to synthesize silicalite-1 from clear solution mixtures comparable to those previously investigated (i.e. 1:0.36:20 TEOS:TPAOH:H2O (TEOS = tetraethyl orthosilicate; TPAOH = tetrapropylammonium hydroxide), 368 K). All TPAOH-organosiloxane mixtures studied form silica nanoparticles after aging at room temperature for 24 h. Full-profile fitting analysis of the SAXS data indicates the particles are ellipsoidal and is inconsistent with the presence of "nanoslabs" or "nanoblocks". Synthesis using TEOS as the silica source have an induction period of approximately 7.5 h and a growth rate of 1.90 +/- 0.10 nm/h at 368 K. Changing the silica source to tetramethyl orthosilicate (TMOS) does not change the induction period; however the particle growth rate is decreased to 1.65 +/- 0.09 nm/h at 368 K. Variable-temperature SAXS measurements for syntheses with TEOS and TMOS show the activation energy for silicalite-1 growth is 60.0 +/- 2.9 and 73.9 +/- 2.8 kJ/mol, respectively, indicating the alcohol identity does influence the growth rate. By mixing tetrapropyl orthosilicate (TPOS) with TEOS (1.6:1.0 molar ratio) as the silica source, the precursor solution shows a shorter induction period (6.0 h) and a faster particle growth rate (2.16 +/- 0.06 nm/h). The alcohol identity effect is more pronounced when other organocations (e.g. alkyltripropylammonium cations) are used to make silicalite-1 at 368 K. Removing ethanol from the precursor solution decreases the induction period to approximately 4.5 h and increases the particle growth rate to 2.99 +/- 0.13 nm/h. Mixtures with 2 equiv of ethanol have an induction period and particle growth rate of 6.0 h and 2.04 +/- 0.03 nm/h, respectively. The results demonstrate the alcohol identity and content influence silicalite-1 growth kinetics. One possible explanation is varying the alcohol identity and content changes the strength of the hydrophobic hydration of the structure-directing agent and the water-alcohol interaction, resulting in less efficient interchange between clathrated water molecules and solvated silicate species.