2 sentences for 徒 (tú — in vain)

1. 少壮不努力，老大徒伤悲。

   shào​zhuàng bù nǔ​lì, lǎo​dà tú shāng​bēi.

   If one does not work hard in youth, one will grieve in vain in old age.

   Source: Dong Chinese Dictionary

2. 望着满地的落叶，他心中徒增几分感伤。

   wàng zhe mǎn​dì de luò​yè, tā xīn​zhōng tú zēng jǐ fēn gǎn​shāng.

   Gazing at the fallen leaves everywhere, he felt an added sense of melancholy.

   Source: Dong Chinese Dictionary