Hi, most of your sentences is right grammartically, but some of them sounds werid in their meaning.
(2) 只有到了黄山， 。
(1) 只有保护好环境，(我们才 would be better)将生活在一个纯洁的世界.
(2) 黄山 is a place of interest in china, it's famouse for its beauty.
(3) 只有他,才能很好地研究中国文学。(the sentence is right, but the meaning of it is a little werid, it means that only this man in the world knows how to learn the Chinese culture, maybe you can say 'only if you work hard can you...' =只有你付出努力，才能很好地研究中国文学。 )
(4) 只有他，才能练好书法。(same as the third one, the sentence is right, but the meaning of it is a little werid ,it means that only this man in the world have a good handwriting, maybe you can say ' only when you practice much can you...'=只有你当练习足够多的时候，才能练好书法。)
Hope these might help you.