Over the past few decades, researchers have established artificial enzymes as highly stable and low-cost alternatives to natural enzymes in a wide range of applications. A variety of materials including cyclodextrins, metal complexes, porphyrins, polymers, dendrimers and biomolecules have been extensively explored to mimic the structures and functions of naturally occurring enzymes. Recently, some nanomaterials have been found to exhibit unexpected enzyme-like activities, and great advances have been made in this area due to the tremendous progress in nano-research and the unique characteristics of nanomaterials. To highlight the progress in the field of nanomaterial-based artificial enzymes (nanozymes), this review discusses various nanomaterials that have been explored to mimic different kinds of enzymes. We cover their kinetics, mechanisms and applications in numerous fields, from biosensing and immunoassays, to stem cell growth and pollutant removal. We also summarize several approaches to tune the activities of nanozymes. Finally, we make comparisons between nanozymes and other catalytic materials (other artificial enzymes, natural enzymes, organic catalysts and nanomaterial-based catalysts) and address the current challenges and future directions (302 references).

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes

This Review focuses on noncovalent functionalization of graphene and graphene oxide with various species involving biomolecules, polymers, drugs, metals and metal oxide-based nanoparticles, quantum dots, magnetic nanostructures, other carbon allotropes (fullerenes, nanodiamonds, and carbon nanotubes), and graphene analogues (MoS2, WS2). A brief description of π–π interactions, van der Waals forces, ionic interactions, and hydrogen bonding allowing noncovalent modification of graphene and graphene oxide is first given. The main part of this Review is devoted to tailored functionalization for applications in drug delivery, energy materials, solar cells, water splitting, biosensing, bioimaging, environmental, catalytic, photocatalytic, and biomedical technologies. A significant part of this Review explores the possibilities of graphene/graphene oxide-based 3D superstructures and their use in lithium-ion batteries. This Review ends with a look at challenges and future prospects of noncovalently modified graph...

/pdf/noncovalent-functionalization-of-graphene-and-graphene-oxide-49z1h0rufs.pdf

Noncovalent Functionalization of Graphene and Graphene Oxide for Energy Materials, Biosensing, Catalytic, and Biomedical Applications

This review article presents the fundamental and practical aspects of water adsorption in Metal–Organic Frameworks (MOFs). The state of the art of MOF stability in water, a crucial issue to many applications in which MOFs are promising candidates, is discussed here. Stability in both gaseous (such as humid gases) and aqueous media is considered. By considering a non-exhaustive yet representative set of MOFs, the different mechanisms of water adsorption in this class of materials are presented: reversible and continuous pore filling, irreversible and discontinuous pore filling through capillary condensation, and irreversibility arising from the flexibility and possible structural modifications of the host material. Water adsorption properties of more than 60 MOF samples are reported. The applications of MOFs as materials for heat-pumps and adsorbent-based chillers and proton conductors are also reviewed. Some directions for future work are suggested as concluding remarks.

/pdf/water-adsorption-in-mofs-fundamentals-and-applications-25siy6wd87.pdf

Water adsorption in MOFs: fundamentals and applications

In this review, we discuss the phenomenon of complementary macropore incorporation into mesoporous and/or microporous solids in order to enhance their catalytic performance in fuels and chemicals synthesis.

Hierarchical porous materials: catalytic applications.

Membrane distillation is a process that utilizes differences in vapor pressure to permeate water through a macro-porous membrane and reject other non-volatile constituents present in the influent water. This review considers the fundamental heat and mass transfer processes in membrane distillation, recent advances in membrane technology, module configurations, and the applications and economics of membrane distillation, and identifies areas that may lead to technological improvements in membrane distillation as well as the application characteristics required for commercial deployment.

/pdf/advances-in-membrane-distillation-for-water-desalination-and-1u0f2j17hn.pdf

Advances in Membrane Distillation for Water Desalination and Purification Applications

Graphene oxide–iron oxide (GO–Fe3O4) nanocomposites were synthesised by co-precipitating iron salts onto GO sheets in basic solution. The results showed that formation of two distinct structures was dependent upon the GO loading. The first structure corresponds to a low GO loading up to 10 wt%, associated with the beneficial intercalation of GO within Fe3O4 nanoparticles and resulting in higher surface area up to 409 m2 g−1. High GO loading beyond 10 wt% led to the aggregation of Fe3O4 nanoparticles and the undesirable stacking of GO sheets. The presence of strong interfacial interactions (Fe-O-C bonds) between both components at low GO loading lead to 20% higher degradation of Acid Orange 7 than the Fe3O4 nanoparticles in heterogeneous Fenton-like reaction. This behaviour was attributed to synergistic structural and functional effect of the combined GO and Fe3O4 nanoparticles.

/pdf/structural-and-functional-investigation-of-graphene-oxide-hh6joa688y.pdf

Structural and functional investigation of graphene oxide–Fe3O4 nanocomposites for the heterogeneous Fenton-like reaction

The sacrificial role of graphene oxide in stabilising a Fenton-like catalyst GO–Fe3O4

Long term pervaporation desalination of tubular MFI zeolite membranes

Here we show the long term performance at high temperatures of a multi-tube module containing 8 membranes in 4 parallel lines with a total of 545 cm2 area. The membranes were prepared via thin film dip coating of cobalt oxide silica (CoOxSi) sol–gel on tubular alumina supports. A preliminary study found that the sol–gel containing 20 mol% cobalt oxide formed the best microporous structure with the highest surface area and pore volume. All resulting membranes delivered permeances of ∼1 × 10−7 mol m−2 s−1Pa−1 at 500 °C, indicating a high repeatability for the membrane fabrication process. The permselectivities of helium (He) and hydrogen (H2) over carbon dioxide (CO2) and nitrogen (N2) increased from 10–20 at 100 °C to values close to 1000 at 500 °C. Additionally, the apparent energies of activation (Eact) for the smaller kinetic diameter gases He and H2 at 12.2 and 19.5 kJ mol−1 were high and contrary to the negative values for larger gases N2 and CO2 at −1.8 and −7.4 kJ mol−1. These remarkable results were attributed to the molecular sieving mechanism of the microporous silica which was enhanced by the embedding of cobalt oxide into the matrix, delivering structural control with an average pore size of 3 A. The Eact for H2 permeance was higher than that of He, indicating that the cobalt oxide played an important role in H2transport. Two membrane lines performed exceptionally well for binary gas mixture processing with H2 purity reaching values close to 100% in the permeate stream for argon (Ar) concentrations of up to 80% in the retentate stream. A major finding here is that the binary gas selectivity was independent of temperature, contrary to the permselectivity observed for single gas permeance. Further, the H2 flow rate was greatly affected by the concentration of Ar in the mixture, while the temperature dependency played only a marginal role. In particular, competitive adsorption in the percolative pathways containing pore constrictions or bottlenecks of the anisotropic CoOxSi matrix allowed Ar to impede H2 diffusion. Finally, the CoOxSi membranes proved thermally stable and robust for 2000 h of testing for various thermal cycles up to 500 °C.

Long term performance cobalt oxide silica membrane module for high temperature H2 separation

This review provides a global overview of microporous silica based membranes for desalination via pervaporation with a focus on membrane synthesis and processing, transport mechanisms and current state of the art membrane performance. Most importantly, the recent development and novel concepts for improving the hydro-stability and separating performance of silica membranes for desalination are critically examined. Research into silica based membranes for desalination has focussed on three primary methods for improving the hydro-stability. These include incorporating carbon templates into the microporous silica both as surfactants and hybrid organic-inorganic structures and incorporation of metal oxide nanoparticles into the silica matrix. The literature examined identified that only metal oxide silica membranes have demonstrated high salt rejections under a variety of feed concentrations, reasonable fluxes and unaltered performance over long-term operation. As this is an embryonic field of research several target areas for researchers were discussed including further improvement of the membrane materials, but also regarding the necessity of integrating waste or solar heat sources into the final process design to ensure cost competitiveness with conventional reverse osmosis processes.

/pdf/microporous-silica-based-membranes-for-desalination-39a5pkzi8f.pdf

Christelle Yacou

Papers

Structural and functional investigation of graphene oxide–Fe3O4 nanocomposites for the heterogeneous Fenton-like reaction

The sacrificial role of graphene oxide in stabilising a Fenton-like catalyst GO–Fe3O4

Long term pervaporation desalination of tubular MFI zeolite membranes

Long term performance cobalt oxide silica membrane module for high temperature H2 separation

Microporous Silica Based Membranes for Desalination