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@ARTICLE{Ayalew:422544,
      author       = {Ayalew, Eyasu and Janssens, Koen and De Wael, Karolien},
      title        = {{U}nraveling the {R}eactivity of {M}inium toward
                      {B}icarbonate and the {R}ole of {L}ead {O}xides {T}herein},
      journal      = {Analytical chemistry},
      volume       = {88},
      number       = {3},
      issn         = {1520-6882},
      address      = {Columbus, Ohio},
      publisher    = {American Chemical Society},
      reportid     = {PUBDB-2019-02230},
      pages        = {1564 - 1569},
      year         = {2016},
      note         = {© American Chemical Society; Post referee fulltext in
                      progress 2; Embargo 12 months from publication},
      abstract     = {Understanding the reactivity of (semiconductor) pigments
                      provides vital information on how to improve conservation
                      strategies for works of art to avoid rapid degradation of
                      the pigments. This study focuses on the photoactivity of
                      minium (Pb$_3$O$_4$), a semiconductor pigment that gives
                      rise to strong discoloration phenomena upon exposure to
                      various environmental conditions. For demonstrating its
                      photoactivity, an electrochemical setup with a
                      minium-modified graphite electrode (C|Pb$_3$O$_4$) was used.
                      It is confirmed that minium is a p-type semiconductor that
                      is photoactive during illumination and becomes inactive in
                      the dark. Raman measurements confirm the formation of
                      degradation products. The photoactivity of a semiconductor
                      pigment is partly defined by the presence of lead oxide
                      (PbO) impurities; these introduce new states in the original
                      band gap. It will be experimentally evidenced that the
                      presence of PbO particles in minium leads to an upward shift
                      of the valence band that reduces the band gap. Thus, upon
                      photoexcitation, the electron/hole separation is more easily
                      initialized. The PbO/Pb$_3$O$_4$ composite electrodes
                      demonstrate a higher reductive photocurrent compared to the
                      photocurrent registered at pure PbO or Pb$_3$O$_4$-modified
                      electrodes. Upon exposure to light with energy close to and
                      above the band gap, electrons are excited from the valence
                      band to the conduction band to initialize the reduction of
                      Pb(IV) to Pb(II), resulting in the initial formation of PbO.
                      However, in the presence of bicarbonate ions, a
                      significantly higher photoreduction current is recorded
                      because the PbO reacts further to form hydrocerussite.
                      Therefore, the presence of bicarbonates in the environment
                      stimulates the photodecomposition process of minium and
                      plays an important role in the degradation process.},
      cin          = {DOOR},
      ddc          = {540},
      cid          = {I:(DE-H253)HAS-User-20120731},
      pnm          = {6G3 - PETRA III (POF3-622)},
      pid          = {G:(DE-HGF)POF3-6G3},
      experiment   = {EXP:(DE-H253)P-P06-20150101},
      typ          = {PUB:(DE-HGF)36 / PUB:(DE-HGF)16},
      pubmed       = {pmid:26720157},
      UT           = {WOS:000369471100014},
      doi          = {10.1021/acs.analchem.5b02503},
      url          = {https://bib-pubdb1.desy.de/record/422544},
}