It would be beneficial to determine what HM or metalloid has an impact on a particular area. Some researchers uses a HM or metalloid that are popular while others may use a lesser known metal or metalloid. This way you could develop your own niche.
However, you probably do not want to delve into a laboratory study where an element is highly toxic since you will have to get rid of the waste & you or peers may be subjected to it.
If you meant adsorbent, it really depends on what you want to remove. Do a search as there is much research and many papers written on this topic.
Take a look on the following link, here you can find a quite number of published work which is strongly correlated with your query & topic.
https://www.researchgate.net/profile/Md-Rahman-1070?ev=hdr_xprf
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