Smart self-healing coatings for corrosion protection of metallic substrates (steel, magnesium, and aluminium, and their alloys) have attracted tremendous interest due to their capability to prevent crack propagation in the protective coatings by releasing active agents from micro/nanocapsules, that is, micro/nano particles consisting of a coating layer or a shell (micro/nanocontainers) and core material (solids, droplets of liquids or gases), in a controllable manner. This paper aims to give a concise review on the most recent advances in preparing micro/nanocapsules based on different types of micro/nanocontainers, i.e., organic polymer coatings, inorganic clays, mesoporous silica nanoparticles, polyelectrolyte multilayers, etc. for smart coatings with self-healing properties. The state-of-the-art design and preparation of micro/nanocapsules are highlighted with detailed examples.

Polymer nanocomposites exhibit unique physicochemical properties that cannot be obtained with individual components acting alone. Polymer nanocomposites have attracted significant research interests due to their promising potential for versatile applications ranging from environmental remediation, energy storage, electromagnetic (EM) absorption, sensing and actuation, transportation and safety, defense systems, information industry, to novel catalysts, etc. In particular, polymer nanocomposites have attracted intensive research interest for solving both energy and environmental issues. This review paper mainly focuses on the most recent advances in polymer nanocomposites for energy storage (i.e., electrochemical capacitors and batteries), energy saving (i.e., electrochromic devices and carbon dioxide capture), and anticorrosion (conductive and non-conductive polymer nanocomposite anticorrosive coatings) applications.

Magnetic carbon–iron nanoadsorbents fabricated by carbonizing cellulose and reducing Fe₃O₄ nanoparticles or Fe(NO₃)₃ (the products are denoted as MC–O and MC–N, respectively) have demonstrated great Cr(VI) removal. MC–N with a higher proportion of zero-valence iron (ZVI) and bigger specific surface area exhibited better resistance to oxygen and acid than MC–O due to its smaller pore size. The Cr(VI) removal was highly pH-dependent. For example, 4.0 mg L⁻¹ Cr(VI) neutral solution was completely purified by 2.5 g L⁻¹ MC–O and MC–N within 10 min. 1000 mg L⁻¹ Cr(VI) solution at pH 1.0 was completely removed by both nanoadsorbents in 10 min. The MC–O nanoadsorbents had a higher removal percentage (98.1%) than MC–N (93.5%) at pH 7.0, while MC–N had a removal capacity of 327.5 mg g⁻¹, much higher than 293.8 mg g⁻¹ of MC–O at pH 1.0. A chemical adsorption was revealed from the pseudo-second-order kinetic study. Monolayer adsorption of Cr(VI) was revealed by a better fitting of the Langmuir model isotherm, rather than multilayer adsorption for the Freundlich model. These nanoadsorbents could be easily separated from solution by using a permanent magnet after being treated with Cr(VI). Finally, the Cr(VI) removal mechanisms were proposed considering the Cr(VI) reduction and precipitation of Cr(III).

Asymmetric supercapacitors with CNT@nickel hydroxide nanosheet composites and 3-D graphene networks demonstrated a high energy density (∼44.0 W h kg ⁻¹ ) and high power density (∼16 kW kg ⁻¹ ) in aqueous KOH electrolyte.

Magnetic carbon nanoadsorbents fabricated by using cellulose and Fe(NO₃)₃ as the carbon and iron precursors have demonstrated great Cr(VI) removal performance. The magnetic carbon synthesized at a carbonization temperature of 700 °C and a heating rate of 10 °C min⁻¹ (MC7–10) has a greater Cr(VI) removal capacity (22.8 mg g⁻¹) in neutral solutions due to its larger specific surface area (247.14 m² g⁻¹). Moreover, the magnetic carbon fabricated at a carbonization temperature of 800 °C and a heating rate of 10 °C min⁻¹ (MC8–10) has the highest Cr(VI) removal capacity (278.8 mg g⁻¹) in acidic solutions, much higher than those of cellulose (12.0 mg g⁻¹), zero valent iron (ZVI)/chitosan (55.8 mg g⁻¹) and ZVI doped ordered mesoporous carbon (256.86 mg g⁻¹). The high removal capacity was attributed to its higher content of ZVI and specific surface area (136.27 m² g⁻¹) of MC8–10. The reduction of Cr(VI) to Cr(III) by the oxidation of carbon layer as well as the ZVI in the acidic solution was verified as the main mechanism for Cr(VI) removal. Moreover, the nanoadsorbents could be easily separated from solution by using a permanent magnet after being treated with Cr(VI).

The growth mechanism of magnetic nanoparticles (NPs) in the presence of graphite oxide (GO) has been investigated by varying the iron precursor dosage and reaction time (product donated as MP/GO). The synthesized magnetic NPs were anchored on the GO sheets due to the abundant oxygen-containing functionalities on the GO sheets such as carboxyl, hydroxyl and epoxy functional groups. The introduced NPs changed the intrinsic functionalities and lattice structure of the basal GO as indicated by FT-IR, Raman and XRD analysis, and this effect was enhanced by increasing the amount of iron precursor. Uniform distribution of NPs within the basal GO sheets and an increased particle size from 19.5 to 25.4, 31.5 and 85.4 nm were observed using scanning electron microscope (SEM) and transmission electron microscope (TEM) when increasing the weight ratio of GO to iron precursor from 10 : 1, to 5 : 1, 1 : 1 and 1 : 5, respectively. An aggregation of NPs was observed when increasing the iron precursor dosage or prolonging the reaction time from 1 to 8 h. Most functionalities were removed and the magnetic NPs were partially converted to iron upon thermal treatment under a reducing condition. The GO and MP/GO nanocomposites reacted for one and two hours (denoted as MP/GO₁-1 h and MP/GO₁-2 h) were converted from insulator to semiconductor after the annealing treatment as annealed GO (A-GO, 8.86 S cm⁻¹), annealed MP/GO₁-1 h (A-MP/GO₁-1 h, 7.48 × 10⁻² S cm⁻¹) and annealed MP/GO₁-2 h (A-MP/GO₁-2 h, 7.58 × 10⁻² S cm⁻¹). The saturation magnetization was also enhanced significantly after the annealing treatment, increased from almost 0 to 26.7 and 83.6 emu g⁻¹ for A-MP/GO₁-1 h and A-MP/GO₁-2 h, respectively.