Fig. 1

SEM images of raw volcanic tuff (VT) (a), treated with acid (VT1) (b) or treated with iron (Fe_VT) (c), as well as Fe_VT after five cycles of reuse with RB5 in the absence of hydrogen peroxide (d) or with 10 mM H2O2 (e).

SEM images of raw volcanic tuff (VT) (a), treated with acid (VT1) (b) or treated with iron (Fe_VT) (c), as well as Fe_VT after five cycles of reuse with RB5 in the absence of hydrogen peroxide (d) or with 10 mM H2O2 (e).