TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Process: The formation of in-situ hydrogel involves single-step process. The manufacture of aerogel involves controlling reaction time and/or concentration involved in the hydrothermal process to affect formation of the hydrogel. The concentration of the reaction mixture is controlled, so that particulates in the in-situ hydrogel are not aggregated. The temperature and/or pressure involved in the hydrothermal process are controlled to affect the formation of the hydrogel. The suspension or solution is subjected to ultrasonic processing and/or filtering before subjecting to hydrothermal and solvothermal process. The liquid is removed from the hydrogel by freeze drying, supercritical point drying, and/or drying in an ambient condition. The usage method of aerogel further involves absorption, ion-exchanging reaction, redox and/or photo-catalytic redox reaction, subjecting a concentration of a suspension or a solution comprising a concentration of one or more chemical reactant to hydrothermal and/or solvothermal process for a reaction time to form an in-situ hydrogel, removing a liquid from the hydrogel to form an aerogel, arranging a coating comprising one or more hydrophobic surface on portion(s) of surface of the composition. Preferred Composition: The in-situ hydrogel comprises a metal, an oxide, a nitride, a sulfide, a semiconductor, and/or a carbon-containing material. The in-situ hydrogel comprises manganese dioxide, titanium oxide, zinc oxide, zirconium oxide, copper oxide, and/or chromium oxide. The particulates are in the form of three-dimensional network. Preferred Properties: The particulates have length of 100 microns or more, and diameter of 500 nm or less. The composition has density of 16 mg/cm3 or more, and Young's modulus of 25 MPa or more, and tensile strength of 1.1 MPa or more. The composition has density of 4 mg/cm3 or more, Young's modulus of 2.5 MPa or more, tensile strength of 0.1 MPa or more, compressive strain of 90% or more, and maximum compressive stress of 0.035 MPa or more.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The fluid comprises Water, and the component comprises oil, solvent, metal-containing ions, microbes, microorganisms and/or organic compound, and/or oil, smog, organic compound, air-born microbes and/or microorganism. The component comprises oil and the composition exhibits a weight-to-weight absorption capacity of the component of 250 or more.