Anaerobic oxidation of methane (AOM) is one of the major processes of oxidizing methane in marine sediments. Up to now, extensive studies about AOM coupled to sulfate reduction have been conducted because SO₄²⁻ is the most abundant electron acceptor in seawater and shallow marine sediments. However, other terminal electron acceptors of AOM, such as NO₃⁻, NO₂⁻, Mn(IV), Fe(III), are more energetically favorable than SO₄²⁻. Iron oxides, part of the major components in deep marine sediments, might play a significant role as an electron acceptor in the AOM process, mainly below the sulfate–methane interface, mediated by physiologically related microorganisms. Iron-coupled AOM is possibly the dominant non-sulfate-dependent AOM process to consume methane in marine ecosystems. In this review, the conditions for iron-coupled AOM are summarized, and the forms of iron oxides as electron acceptors and the microbial mechanisms are discussed.

One-dimensional (1D) structured sodium titanate (Na-titanate) derived from the NaOH treatment of TiO₂ nanoparticles under highly basic conditions are widely used as precursors to prepare TiO₂ with various crystalline phases, shapes, sizes or exposed facets. However, potassium ions in the potassium titanate (K-titanate) structure couldn't be fully exchanged by protons, therefore only a few studies have been conducted on the preparation of pure TiO₂ from K-titanate precursor. In this paper, we report that K-titanate could be fully transferred to pure TiO₂ through hydrothermal reaction in acidic solution. As a result, pure phase and mixtures of four TiO₂ polymorphs (anatase, rutile, brookite, and TiO₂(B)) could be controllably obtained. The transformation mechanism from K-titanate to TiO₂ counterparts was proposed. In addition, the photocatalytic activities of TiO₂ nanocrystals with different crystalline-phase composition have been investigated, and the mixed-phase samples showed much higher photocatalytic activity than either of the pure component phases.