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Table 1 Physico-chemical characterization of the 14 test materials (i.e. 13 nanomaterials and micron-scale ZnO)

From: Application of short-term inhalation studies to assess the inhalation toxicity of nanomaterials

  Al-doped CeO2 CeO2 Uncoated ZrO2 Nano-BaSO4NM-220 TiO2(T-Lite SF™) coated nano-ZnO NM-111 micron-scale ZnO SiO2. naked SiO2. acrylate SiO2. PEG SiO2. amino SiO2. phosphate ZrO2. acrylate ZrO2. TODA
PPS/shape (TEM; nm) 2-160 globular 0-200 globular 25-60 globular 25 globular 15 × 50 Aspect ratio >3, fiber 20-200 mostly globular 50 – 500 globular 15 20 15 15 15 9 9
Agglomerate size/shape (SEM; nm) >20,000 >10,000 1,000 - 5,000 2,800 - 15,000; spheres   >20,000 2,500        
Crystallite size (XRD; nm) 23 36 45 36 24 61 >100 n.a. n.a. n.a. n.a. n.a. n.a. n.a.
Crystalline phase (XRD) Cerianite cubic Cerianite cubic ZrO2 tetragonal Barite orthorhombic Rutile, (minimally anatase) Zincite, ZnO hexagonal Zincite, ZnO hexagonal n.a. n.a. n.a. n.a. n.a. n.a. n.a.
Pore sizes (Hg porosimetry; nm) 30; 800; 40,000 30; 20,000 40; 1,000; 15,000 30; 5,000 20; 30,000 30; 40,000 5; 200; 7,000 n.a. n.a. n.a. n.a. n.a. n.a. n.a.
Specific surface area (BET nitrogen adsorption and Hg intrusion porosimetry; m2/g) 46.0 (62) 33.0 (34) 24.9 (29) 41.4 (33) 100.0 (82) 12.0 (20) 5.6 (55) n.a. n.a. n.a. n.a. n.a. n.a. n.a.
Surface chemistry (XPS; supported by SIMS; as necessary; Atom%/qualitative) Ce: 21; Al: 9; O: 56; C: 9; Zr: 4; N: 1 Ce: 16; O: 61; C: 9 (C-C, O-C = O); Al: 9; Zr: 5 Zr: 24; O: 53; C: 19 (C-C, C-O, O-C = O); N: 3; Al: 1 Ba: 13; O; 52; C: 17; S: 11; Cl: 3; P: 3; N: 1 Ti: 16; O: 63; C: 9; Al: 7; Si: 5; Na: <1; dimethicone/methicone copolymer as surface coating Zn: 1; C: 64; (C-C, C-O, peptide) O: 19; N: 12; Na: 2; P: 2; Cl: 1; 3.5% triethoxy-octylsilane n/d Si: 29; O: 66; C: 4 (C-C, C-H, C-O, C = O) Na: 1 Si: 21; O: 54C: 24 (C-C, some C-O, C = O); Na: 1; SIMS: poly-methacrylic acid/3-methac-ryloxypropyl SIMS: expected fragments of PEG500 (CH2CH2O) SIMS: expected fragments of aminosilane Si: 29; O: 66; C: 4.6; Na: 0.5; expected P, N not detec-ted by XPS, but PO2, PO3 fragments by SIMS Zr 23; O: 58; C: 19; SIMS: expected acrylic acid Zr; 24; O: 63; C: 11; N: 0.7; S: 0.2; SIMS: expected trioxa-decanoic acid
Photocatalysis: photon efficiency, unitlessa 8.8E-04 1.6E-03 7.0E-04 1.1E-03 5.3E-04 n.m. (hydrophobic) 5.0E-01 1.7E-5 5.9E-5 6.2E-5 8.8E-5 1.9E-4 2.9E-5 5.8E-5
Surface charge Iso-electric point/Mobility at pH 7 8.5/1.4 (μm/s)/V/cm) 7.5/0.5 (μm/s)/V/cm) 6.5/-0.9 (μm/s)/V/cm) 3.3/-2.2 (μm/s)/V/cm) 6.5/-0.2 (μm/s)/V/cm) n.m. (agglo-merated) n.m. (agglo-merated) <1/- <1/- 4/- 7.2/- <1/- <1/- 7.1/-
Zeta-potential at pH 7 (mV) 18 6 −12 −28 −3    −38 −47 −26 0 −43 −39 −6
Surface reactivity (ESR + CPH)b         4 (p-f s: 0.8) n.d. 1 (p-f s: 3.4) 1 (p-f s: 1.1) 2.2 (p-f s: 1.2) 1 (p-f s: 2) 0.54 (p-f s: 5.7)
Formation of OH radicals (ROS) ESR + DMPOb         11 (p-f s: 6.3) n.d. 11 (p-f s: 13) 21 (p-f s: 5.2) 19 (p-f s: 5) 3.6 (p-f s: 1.5) 0.94 (p-f s: 1.3)
Particle size/dispersability in water 603/20 90/3.0 1,500/38; <0.1 wt% <100 nm 116/4.6 33/1.7 Agglom.; <0.01 wt% <100 nm 5,100 /20; <0.1 wt% <100 nm 19/1 23/1 21/1 20/1 20/1 27/3 11/1
in DMEM/FCS (AUC; D50 (nm)/AAN (qualitative)) 94/3.1 54/1.8 87/2.2 285/11 3,900/195; 2 wt% <100 nm 550/18 950/3.8 420/28 26/1 3200/213 1350/90 30/2 315/32 860/86
Solubility in water and in DMEM/FCS Ce, Al <0.1 ppm Ce <0.1 ppm Zr <0.1 ppm Ba 6 ppm Ti 5 ppm Ti 5 ppm Soluble at pH < 6 Zn <5 ppm Zn 50 ppm        
  1. aCatalytic events per photon impinging on the surface, as specified in DIN 52980.
  2. bSurface reactivity and ROS formation were determined relative to the ‘reference material’ deuterium oxide (D2O; 2H2O). Assuming a 30% variability of the methodology, only measurements >1.3 are considered relevant. Of note, this value should only serve as a guiding principle, and not as an absolute value.
  3. Abbreviations: AAN average agglomeration number; derived from the ratio of the volume-based median particle size to the average equivalent spherical volume derived from the BET gas adsorption, AUC analytical ultracentrifugation, BET method of Brunauer-Emmett-Teller, D50 medium value of the particle size distribution, DMEM/FCS Dulbecco’s Modified Eagle Medium supplemented with 10% fetal calf serum, ESR + CPH Electron spin resonance making use of centrophenoxine spin traps, ESR + DMPO Electron spin resonance making use of dimethyl-pyrroline-N-oxide spin traps, n.a. not applicable, n.d. not determined, n.m. not measurable, p-f s particle-free supernatant, PPS primary particle size, ROS reactive oxygen species, SEM scanning electron microscopy, SIMS secondary ion mass spectrometry, TEM transmission electron microscopy, XPS x-ray photoelectron spectroscopy, XRD x-ray diffusion.