Ubuntu :: Encoding Conversion On Multiple Files?

I'm trying to convert the encoding of multiple files in a directory and I try to do it as follows.

Code:
#/bin/bash
find . -type f -name *.txt -exec iconv -f GBK -t utf-8 "{}" -o "{}.utf8" ;
find . -type f -name *.utf8 -exec mv -f "{}" `echo "{}" | sed 's/.utf8//'` ;

The first command goes well by generating utf8 files from all txt files, but the second command fails with error message. Could someone enlighten me about the mistake in the command and share a workable solution?