So, after the Opium War, Britain forced China to open a bit and, though the Chinese court would remain in denial that the West had surpassed them technologically for a few decades more, I know some Chinese could see the writing in the wall and tried to push their country to modernize.
My question is: Is there any accounts of the first Chinese to visit Europe post-First or Second Opium War? How did they describe the new technology, the society, the culture?
Extra question, answer if you want: What about the huge European colonial empires? Did the Chinese express any opinion about them and about what they should do about it?
Your chronology's a bit off there: Chinese people were well aware of British industrialisation and technological capacity before the Opium War. The popular narrative of Chinese naïveté is simply wrong. The latter part of this answer goes into firsthand accounts of Britain by Chinese travellers and secondhand conclusions by Chinese scholars during the late 18th and early 19th centuries.