  This paper investigates eleven (UV-)optical-infrared (IR) spectral energy
distributions (SEDs) of six tidal disruption events (TDEs), which are
ASASSN-14li, ASASSN-15lh, ASASSN-18ul, ASASSN-18zj, PS18kh, and ZTF18acaqdaa.
We find that all the SEDs show evident IR excesses. We invoke the blackbody
plus dust emission model to fit the SEDs, and find that the model can account
for the SEDs. The derived masses of the dust surrounding ASASSN-14li,
ASASSN-15lh, ASASSN-18ul, ASASSN-18zj, PS18kh, and ZTF18acaqdaa are
respectively $\sim0.7-1.0\,(1.5-2.2)\times10^{-4}\,M_\odot$,
$\sim0.6-3.1\,(1.4-6.3)\times10^{-2}\,M_\odot$,
$\sim1.0\,(2.8)\times10^{-4}\,M_\odot$,
$\sim0.1-1.6\,(0.3-3.3)\times10^{-3}\,M_\odot$,
$\sim1.0\,(2.0)\times10^{-3}\,M_\odot$, and $\sim
1.1\,(2.9)\times10^{-3}\,M_\odot$, if the dust is graphite (silicate). The
temperature of the graphite (silicate) dust of the six TDEs are respectively
$\sim1140-1430\,(1210-1520)$\,K, $\sim1030-1380\,(1100-1460)$\,K,
$\sim1530\,(1540)$\,K, $\sim960-1380\,(1020-1420)$\,K, $\sim900\,(950)$\,K, and
$\sim1600\,(1610)$\,K. By comparing the derived temperatures to the
vaporization temperature of graphite ($\sim 1900$\,K) and silicate ($\sim
1100-1500$\,K), we suggest that the IR excesses of PS18kh can be explained by
both the graphite and silicate dust, the rest five TDEs favor the graphite dust
while the silicate dust model cannot be excluded. Moreover, we demonstrate the
lower limits of the radii of the dust shells surrounding the six TDEs are
significantly larger than those of the radii of the photospheres at the first
epochs of SEDs, indicating that the dust might exist before the the TDEs
occurred.
