Sustainable Chemical Synthesis for Phosphorus-Doping of TiO₂ Nanoparticles by Upcycling Human Urine and Impact of Doping on Energy Applications

Abstract

Recently, there has been significant research interest toward sustainable chemical synthesis and processing of nanomaterials. Human urine, a pollutant, requires energy intensive processing steps prior to releasing into rivers and oceans. Upcyling urine has been proposed and practiced as a sustainable process in the past. Doping is one of the foremost processes to elevate the functionality of nanomaterials depending on the applications it is sought for. Phosphorus doping in to TiO2 nanomaterials has been of research interest over a decade now, that has been chiefly done using acidic precursors. Here we demonstrate, upcycling urine, a sustainable process for phosphorus doping into TiO2 lattice. Upon doping the changes in morphology, surface chemistry and band gap is studied in detail and compared with undoped TiO2 that is prepared using deionized water instead of urine. X-ray photoelectron spectroscopy confirmed that the P was replacing Ti in the lattice and exists in P5+ state with a quantified concentration of 2.5–3 at %. P-doped nanoparticles were almost 50% smaller in size with a lower concentration of surface −OH groups and a band gap increase of 0.3 eV. Finally, impact of these changes on energy devices such as dye-sensitized solar cells and li-ion batteries has been investigated. It is confirmed that P-doping induced surface chemical and band gap changes in TiO2 affected the solar cell characteristics negatively, while the smaller particle size and possibly wider surface channels improved Li-ion battery performance.

Efficient Phosphorus Doping into the Surface Oxide Layers on TiN to Enhance Oxygen Reduction Reaction Activity in Acidic Media

“…50 A single peak was observed at 133−134 eV in the P 2p region, which is assigned to pentavalent phosphorus (P 5+ ) atoms substituted for titanium atoms in the TiO 2 lattice. 55,56 When phosphorusfree TiO x N y catalysts were synthesized under identical conditions, i.e., N 2 pyrolysis at 1123 K without adding a phosphorus source, the Ti 2p 3/2 peak binding energy was 458.3 eV, 45 which is lower than that of the present TiO x N y P z catalyst series shown in Figure 3i−iii (458.5, 458.6, and 458.6 eV at R P = 0.10, 0.20, and 0.35, respectively). Similar positive shifts in Ti 2p spectra by P 5+ doping were assigned to the Ti−O−P bond, i.e., Ti 4+ atoms were replaced by P 5+ atoms in P-doped TiO 2 55 and P,N-codoped TiO 2 .…”

“…55,56 When phosphorusfree TiO x N y catalysts were synthesized under identical conditions, i.e., N 2 pyrolysis at 1123 K without adding a phosphorus source, the Ti 2p 3/2 peak binding energy was 458.3 eV, 45 which is lower than that of the present TiO x N y P z catalyst series shown in Figure 3i−iii (458.5, 458.6, and 458.6 eV at R P = 0.10, 0.20, and 0.35, respectively). Similar positive shifts in Ti 2p spectra by P 5+ doping were assigned to the Ti−O−P bond, i.e., Ti 4+ atoms were replaced by P 5+ atoms in P-doped TiO 2 55 and P,N-codoped TiO 2 . 56 No peak was observed at approximately 129 eV in the P 2p spectra shown in Figure 3, indicating the absence of anionic P 3− species.…”

Interface‐Induced Pseudocapacitance in Nonporous Heterogeneous Particles for High Volumetric Sodium Storage

“…Moreover, the high‐resolution O 1s exhibits an additional peak located at 531.05 eV, which is attributed to the POTi bonding (Figure 1g). [ 17,18 ] The formation of TiOP species is also confirmed by the shifting of Ti 2p peaks of P‐TiO 2 to higher values compared with those of pristine TiO 2 (Figure S2, Supporting Information). [ 16 ] Thus, phosphorus exists as both elemental red P and titanium phosphate (TiPi) in the heterogeneous P‐TiO 2 particles.…”

Promoted Electrocatalytic Nitrogen Fixation in Fe‐Ni Layered Double Hydroxide Arrays Coupled to Carbon Nanofibers: The Role of Phosphorus Doping

“…[20] After doping, these peaks shift positively to 726.7 and 713.8 eV, which arises from the substitution of iron by more electronegative phosphorus to withdraw electrons from the former. [21] As for the Ni 2p spectrum (Figure 2 b), the two peaks at 874.7 and 857.0 eV are attributed to the Ni 2+ 2p 1/2 and Ni 2+ 2p 3/2 orbitals, respectively. Besides, the two shake-up type peaks at 880.9 and 862.8 eV are indicative of the satellite peaks of Ni 2+ .…”