Barium removal from synthetic natural and produced water using MXene as two dimensional (2-D) nanosheet adsorbent

Adsorptive environmental applications of MXene nanomaterials: a review

“…Aer Pb(II), Cr(VI) is listed as another important heavy metal pollutant in water, and its adsorption behavior on MXenes has also been investigated. Cr(VI) exists in the anionic form, i.e., 48 and Cu(II) ions 49 (two typical pollutants in water), and also applied in experiment. The formation of both Ba-O and Ba-F bonds is found to contribute to the Ba(II) ion adsorption process.…”

Review of MXenes as new nanomaterials for energy storage/delivery and selected environmental applications

“…Adsorption is favored, being feasible, extensively applicable, and relatively low-cost [149]. As is true of graphene-based nanomaterials, MXenes can be intercalated with, and delaminated into, nanosheets; various organics (e.g., urea [150] and methylene blue [42,151]) and heavy metals (e.g., Ba [152], Cr [43], Hg [153], Cu [154], and U [155]) naturally intercalate various MXenes, suggesting that MXenes may be valuable adsorbents; it is thus necessary to understand the interactions between MXenes and contaminants. Aqueous removal of contaminants by MXenes is affected by the nature of the contaminants (e.g., inorganic/heavy metals or organics, size/shape, functional group, hydrophilicity, and charge), the properties of the adsorbent (e.g., surface area, functional group, hydrophilicity, and charge), and water quality (e.g., adsorbate concentration, inorganic/ organic issues, pH, and temperature).…”

“…Methylene blue intercalation with MXenes is possible, given the behaviors of dyes with other layered materials such as graphite oxide [159] and clay nanoadsorbents [160]. X-ray diffraction revealed that the c-lattice constant of the MXene interlayer space (0.7-2 nm) [152] was larger than the methylene blue molecule (1.7 × 0.76 × 0.325 nm 3 (l × w × h) [161]). The interlayer spacing of Ti3C2Tx was expanded by tuning the surface functional groups (from -F to -OH) [151].…”

“…MXenes adsorptively removed various heavy metals (Ba [152], Cr [43], Hg [153], Cu [154], and U [155]) from waters of various qualities. 2D Ti3C2Tx nanosheets removed > 99% of Ba 2+ under optimized conditions; the adsorption capacity was 9.3 mg/g [152]. The pH was important during adsorption, because it affects adsorbent surface charge and both speciation and ionization [162].…”

“…In general, maximum Ba 2+ adsorption onto Ti3C2Tx nanosheets was evident at pH 6-7 because: (i) at acidic pH values, MXenes with less-negative surfaces (the pH point of zero charge = pH 2.7 [154]) exhibited lower affinities for heavy metal actions; (ii) at neutral pH, the MXenes were negatively charged, modulated principally by electrostatic attraction; and (iii) at basic pH values, Ba(OH)2 precipitated, and was thus removed from the bulk solution [163]. Figure 5 shows adsorption of Ba 2+ onto MXene surfaces: (i) adsorption occurred in intercalated and unstacked MXene interlayers [164]; and (ii) adsorption was facilitated by -OH, -F, and -O groups on MXene surfaces [152]. Delaminated Ti3C2Tx afforded significantly more Cu 2+ removal (40.9 mg/g) than commercial activated carbon (15.1 mg/g) [154].…”