Manganese　dioxide　(MnO2)　is　a　promising　photo-thermo-electric-responsive　semiconductor　material　for　environmental　applications,　owing　to　its　various　favorable　properties.　However,　the　unsatisfactory　environmental　purification　efficiency　of　this　material　has　limited　its　further　applications.　Fortunately,　in　the　last　few　years,　significant　efforts　have　been　undertaken　for　improving　the　environmental　purification　efficiency　of　this　material　and　understanding　its　underlying　mechanism.　Here,　the　aim　is　to　summarize　the　recent　experimental　and　computational　research　progress　in　the　modification　of　MnO2　single　species　by　morphology　control,　structure　construction,　facet　engineering,　and　element　doping.　Moreover,　the　design　and　fabrication　of　MnO2-based　composites　via　the　construction　of　homojunctions　and　MnO2/semiconductor/conductor　binary/ternary　heterojunctions　is　discussed.　Their　applications　in　environmental　purification　systems,　either　as　an　adsorbent　material　for　removing　heavy　metals,　dyes,　and　microwave　(MW)　pollution,　or　as　a　thermal　catalyst,　photocatalyst,　and　electrocatalyst　for　the　degradation　of　pollutants　(water　and　gas,　organic　and　inorganic)　are　also　highlighted.　Finally,　the　research　gaps　are　summarized　and　a　perspective　on　the　challenges　and　the　direction　of　future　research　in　nanostructured　MnO2-based　materials　in　the　field　of　environmental　applications　is　presented.　Therefore,　basic　guidance　for　rational　design　and　fabrication　of　high-efficiency　MnO2-based　materials　for　comprehensive　environmental　applications　is　provided.