Emulsions play an important role in a number of industrial processes and commercial products where immiscible liquid phases coexist. Recently how to balance the long-term stability and quick demulsification has become a key focus in emulsions. The emergence of stimuli-responsive emulsions has brought a ray of dawn. Over the past decade, CO₂ as alternative of pH has aroused considerable attention in the fields of surfactants and their aggregates, polymers, solvents, as well as microemulsions, because of its renewability, low cost and good biocompatibility. Essentially CO₂ acts as pH, but the former offers more advantages over the latter. However, the focus until recently shifted to the utilization of CO₂ as a trigger for triggering emulsions between "on" (stable) or "off" (unstable) states. These CO₂-responsive emulsions show considerable application potential in oil recovery, emulsion polymerization, extraction separation, cosmetics and other fields, because they can smartly response to the removal or bubbling of CO₂ gas, reflecting in emulsification or demulsification of oil/water mixture. In this review, we highlight the recent advances in this field from general emulsion, Pickering emulsion, and microemulsion, respectively. The principle, performance and applications of the CO₂-responsive emulsion system are introduced in details, and their future development and perspectives are also outlooked.
Contents
1 Introduction
2 CO₂-responsive emulsions/microemulsions
2.1 CO₂-responsive general emulsions
2.2 CO₂-responsive Pickering emulsions
2.3 CO₂-responsive microemulsions
3 Conclusion

As a cross-linked polymeric material with plenty of water inside, polymer hydrogel has been widely used in many fields such as food, cosmetics and biomedicine. However, traditional polymer hydrogel is lack of good mechanical performance, which limits its further applications in high-tech fields. In the past decades, the emergence of a series of high-strength polymer hydrogels with homogenous or special network structures has been improved this situation largely. Among these hydrogels, composite hydrogel, double network hydrogel, Tetra-PEG hydrogel and topological gel are representatives. However, in order to be applied in high-tech fields such as artificial tissues, wearable devices and 3D printing, the hydrogels should possess functionality as well as high strength. Therefore, on the basis of numerous of extensive studies on structures and basic properties of the high-strength polymer hydrogels, functionalizing these high-strength polymer hydrogels has been attracted much attention. Herein, recent progress in functionalization of the high-strength polymer hydrogels has been reviewed, and the four types of high-strength polymer hydrogels mentioned above are mainly involved. Finally, challenges in research and the perspective on the future directions of these fields are briefly discussed.
Contents
1 Introduction
2 Functionalization of high-strength polymer hydrogel
2.1 Functionalization of composite hydrogel
2.2 Functionalization of double network hydrogel
2.3 Functionalization of Tetra-PEG hydrogel
2.4 Functionalization of topological gel
3 Conclusion

In recent years, functional drug delivery systems for both targeting drugs to cancer cells and responding to the specific microenvironmental changes of cancer cells for the delivery of the drug have drawn great attention from the chemistry and pharmacology fields in cancer treatment for minimizing undesired effects in the normal cells. Supramolecular drug delivery systems constructed by noncovalent interactions have the ability to realize dynamic reversible switching of structure, morphology and function in response to various external stimuli, thus, providing a platform for designing and developing smart supramolecular nano-drug carriers. It is clear that supramolecular self-assemblies have been an active area of research and an important component of supramolecular chemistry and nanoscience, novel macrocyclic hosts-based recognition motifs, play extremely important roles in supramolecular self-assemblies and related applications. Moreover, functional groups can be introduced into supramolecular systems through specific modification of hosts or guests, so as to meet the requirements for applications in various fields. By noncovalent functionalization, supramolecular nanosystems will be excellent drug carriers, improving the problems imposed by water solubility and stability of drugs as well as realizing controlled release. In this critical review, we summarize recent results in the investigation of macrocyclic hosts-based supramolecular nanostructures for controllable anticancer drug delivery, and supramolecular drug delivery systems are classified based on the types of macrocyclic frameworks involved. Finally, the prospects are pointed out based on the current development of this system.
Contents
1 Introduction
2 Supramolecular drug delivery systems based on cyclodextrins
2.1 Drug-loaded micelles
2.2 Drug-loaded nanoparticles
2.3 Supramolecular prodrug hydrogels
2.4 Photo-controllable drug delivery vehicles
2.5 Vehicles capable of targeted co-delivery of gene and drug
3 Supramolecular drug delivery systems based on calixarenes
3.1 Drug-loaded vesicles
3.2 Multifunctional co-assemblies
3.3 Amphoteric calixarene-based drug delivery vehicles
4 Supramolecular drug delivery systems based on cucurbiturils
4.1 Drug-loaded vesicles
4.2 Drug-loaded nanoparticles
4.3 Drug-loaded crosslinked supramolecular network
4.4 Molecular container-based drug delivery vehicles
5 Supramolecular drug delivery systems based on pillararenes
5.1 Drug-loaded vesicles or micelles
5.2 Supramolecular prodrug nanoparticles
5.3 Self-imaging drug delivery vehicles
6 Conclusion

Dynamic and reversible interaction is one of important tools for constructing intelligent material systems with controllability and adjustability. However, most of the intelligent systems based on dynamic and reversible interactions only respond to "on/off" transition of external stimuli, including light, heat, solvent, pH, etc., instead of automatic regulation. The development of chemical oscillating reactions and self-oscillating polymer materials provides an important idea for the construction of self-regulated intelligent systems. We introduce dynamic and reversible intelligent systems (DRIS) regulated by chemical oscillating reactions, including autonomous aggregation/disaggregation nanoparticle systems, autonomous assembly/disassembly amphiphilic molecule systems, autonomous assembly/disassembly hydrogel systems, autonomous molecular shuttle systems and autonomous fluorescent oscillation systems, which are constructed base on dynamic and reversible interactions, such as dynamic covalent bonds, host-guest interactions, coordination interactions, ionic interactions and intermolecular interactions. Finally, we prospect the future investigation and development of DRIS regulated by chemical oscillating reactions.
Contents
1 Introduction
2 Chemical oscillating reactions
3 General construction mechanism for DRIS
4 DRIS based on different dynamic and reversible interactions
4.1 DRIS based on dynamic covalent bonds
4.2 DRIS based on host-guest interactions
4.3 DRIS based on coordination interactions
4.4 DRIS based on ionic interactions
4.5 DRIS based on intermolecular interactions
5 Conclusion and outlook

Microgel can change its size under external stimuli, manifesting itself an important building block of intelligent materials. Because light stimulus enables remote control and rapid shifting, photo-responsive materials have drawn great attention of scientists. Introducing photo-responsiveness into microgel has greatly broadened the potential of applications of microgel. This review summarizes recent research progress on light-responsive microgel. Four types of light-responsive microgel are elaborated, including photo-isomerization, photo-thermal, photo-(de)crosslinking, and photo-acidifying. Also, a wide range of applications of light-responsive microgel are reviewed, including light-tuning, drug controlled releasing, information displaying and self-healing hydrogel. At last, a brief outlook on the future development of this field is presented.
Contents
1 Introduction
2 Molecular design of photo-responsive microgel
2.1 Photo-isomerization microgel

Hydrophobic association hydrogels (HA-gels) have physical crosslinking networks, which are generated via hydrophobic association. The synthesis methods, structure optimization, property modulation and applications of HA-gels are becoming hot topics in gel materials. This is because HA-gels have many merits such as high mechanical strength, self healing, secondary processing and so on compared with chemical crosslinking hydrogels. In addition, as network crosslinking points, hydrophobic association domains contain dynamic and reversible association-dissociation balance (RADB). It is worth mentioning that, RADB is not only the highlight of HA-gels, but also the hitting-point and the key of network construct, mechanism study and performance improvement. With advantages of high sensitivity, smart response and biocompatibility, HA-gels have shown promising applications in a lot of fields, including smart materials, biology, medicine, and so on. Therefore, in the review, we begin with structure composition of HA-gels, introduce different structure and synthesis methods of them, and then summarize the cause and mechanism of the differences in properties. At last, the present research status is concluded and the application prospect of HA-gels is outlooked as well.
Contents
1 Introduction
2 Structural composition
2.1 Block hydrophobic association hydrogels
2.2 Coiled-coil peptides hydrophobic association hydrogels
3 Synthesis methods
3.1 Free radical polymerization
3.2 Chemical modification on matrix
4 Performance evaluation
4.1 Mechanical property
4.2 Swelling behavior
4.3 Self healing property
5 Promising applications
5.1 Biology and medicine
5.2 Smart materials
5.3 Oilfield exploitation
6 Conclusion and outlook

Porous organic polymers(POPs) are a class of multi-dimensional network materials, which are built via the strong covalent bonds linkage of various organic building blocks with different geometries and topologies. Recently, POPs become a new rising research field in porous material sciences owning to their advantages of light-weight, large specific surface area, and the pre-designable and precise tuneable structures and functions. POPs have received increasing attention for their tremendous potential applications in gas adsorption/separation, catalysis, photoelectric conversion, sensing, and energy storage, and so on. In this article, recent developments on the controlled synthesis and adjustable performance of POPs are summarized. The application of porous aromatic frameworks and conjugated microporous polymers in adsorption of radioactive iodine is introduced. Meanwhile, some problems and challenges about POPs in this field are also discussed and prospected, respectively.
Contents
1 Introduction
2 Synthesis of porous aromatic frameworks and the
application in adsorption of radioactive iodine
3 Synthesis of conjugated microporous polymers and the application in adsorption of radioactive iodine
4 Conclusion

Due to the tunable Vis-NIR fluorescence and interband fluorescence, β-HgS quantum dots have shown broad application prospects in multi-field such as photoelectric conversion and fluorescence imaging. In this review, the preparation, properties and applications of β-HgS quantum dots are summarized systematically. Firstly, five synthesis methods of β-HgS quantum dots are classified into two categories by solution phase:synthesis in aqueous phase and organic phase. Then, the physical properties of β-HgS quantum dots differing from bulk β-HgS are expounded. Next, the latest applications of β-HgS quantum dots in ion detection, cell imaging, in vivo imaging, light converter and fluorescent ink are summed up. Subsequently, the main two issues existing in the applications of β-HgS quantum dots are pointed out:one is their low photoelectric conversion rate and fluorescence quantum yield for photoelectric device, the other is their poor ability in specific recognition for biomedical fluorescence imaging. Finally, our personal perspectives to solve the problem are outlined that self-assembly aggregates of β-HgS quantum dots could be prepared to improve their photoelectric conversion rate and thermostability; and that chiral biomolecules could be introduced into the surface of β-HgS quantum dots as ligand to obtain chiral β-HgS quantum dots, these chiral β-HgS quantum dots might have potential chiral recognition ability and better biocompatibility which could be used for fluorescence imaging in vitro and in vivo. This review points out a new direction for the development of β-HgS quantum dots.
Contents
1 Introduction
2 Synthesis of β-HgS quantum dots
2.1 Synthesis in organic phase
2.2 Synthesis in aqueous phase
3 Properties of β-HgS quantum dots
3.1 Continuous adjustable fluorescence emission in Vis-NIR band
3.2 Stable electron occupation in the lowest quantum state and interband fluorescence
3.3 Transmission properties for electric magnetic polaron
3.4 High fluorescence quantum yield and good light stability
3.5 Selective recognition ability for metal ion
4 Applications of β-HgS quantum dots
4.1 Heavy metal ion probe
4.2 Cell imaging
4.3 In vivo imaging
4.4 Light converter
4.5 Fluorescent ink
5 Conclusion

Catechol and hydroquinone are important industrial raw materials. The methods by which phenol hydroxylates to dihydroxybenzene (catechol and hydroquinone) by one step are high in utilization of reactant atoms, energy-saving and efficient, which are in line with the concept of sustainable development. Using H₂O₂ as oxidant in the oxidation process of phenol to dihydroxybenzene has become a hot spot in the field of catalytic synthesis because it is simple, environmentally-friendly and it can be done under mild reaction conditions. The catalyst plays a decisive role in this reaction system, and the phenol conversion and yield of the product greatly depend on the catalytic activity of catalyst. In this paper, the recent progresses in the catalysts which are used for the hydroxylation of phenol to dihydroxybenzene are reviewed. According to the reaction system, the catalysts are divided into the catalysts used in thermal-driven reaction systems and in photocatalytic reaction systems. The catalytic performances of the catalysts are mainly evaluated by the conversion of phenol, the selectivity of dihydroxybenzene and stability. The research of metal-containing catalysts in heterogeneous reaction systems using H₂O₂ as oxidant is mainly introduced. Finally, the development trends of application of catalysts in the reaction system of one-step hydroxylation of phenol with H₂O₂ are prospected.
Contents
1 Introduction
2 Catalysts used in thermal-driven reaction systems
2.1 Fe-containing catalysts
2.2 Cu-containing catalysts
2.3 Mixed metal oxide catalysts
2.4 Other metal-containing catalysts
2.5 TS-1 molecular sieve catalysts
2.6 Polyoxometalate compounds
3 Catalysts used in photocatalytic reaction systems
4 Conclusion

Lithium has been regarded as a new kind of strategic energy for its unique physicochemical property with the rapid development of the new energy industry. The demand for lithium increases every year and the lithium extraction and separation technology has attracted more and more interests. China is rich in lithium resource from salt lake brine, but it has not been exploited effectively due to the difficulty by high Mg/Li ratio. Thus, there are crucial research value and strategic significance to study the extraction of lithium from high Mg/Li ratio salt lake brine. In this review, the research status of popular lithium extraction technology from salt lake is summarized, including precipitation, solvent extraction, ion-sieve adsorption, nanofiltration and electrodialysis methods. The advantages and characteristics of the methods above are reviewed and the influence of high Mg/Li ratio on lithium separation is discussed. Moreover, the emerging solvent extraction using ionic liquid extractant and electrodialysis technology with monovalent selective permeability ion exchange membrane used to extract lithium from high Mg/Li ratio salt lake brine are introduced in detail. The two technologies exhibit great research significace and wide application prospects. The former has the potential to develop high effective lithium extractants due to the designability of ionic liquid structure and function. The current research shows that the latter could even reduce the Mg/Li mass ratio from 150 to 8.0 for the simulated brine, and simultaneously, the Li⁺ recovery reaches 95.3%. Finally, the existing problems and development directions of lithium extraction from high Mg/Li ratio salt lake brine in the future are discussed.
Contents
1 Introduction
2 Precipitation method
2.1 Carbonate
2.2 Aluminate
2.3 Aluminium salt
3 Solvent extraction method
3.1 β-Diketones
3.2 Crown ethers
3.3 Organophosphorus
3.4 Ionic liquids
4 Ion-sieve adsorption method
5 Nanofiltration and electrodialysis technology
6 Conclusion